Accelerated self assembly of particles at the air-water interface with optically assisted heating due to an upconverting particle

Muruga Lokesh; Gokul Nalupurackal; Srestha Roy; Snigdhadev Chakraborty; Jayesh Goswami; M. Gunaseelan; M. Gunaseelan; Imdad Uddin Chowdhury; Vidya P. Bhallamudi; Pallab Sinha Mahapatra; Basudev Roy

doi:10.1364/OE.481722

1. Introduction

The capability to create and manipulate assemblies of micro and nano colloidal particles using lasers [1–3] is greatly appreciated in the field of interfacial studies like air-liquid [4], liquid-solid [2], and liquid-liquid [5–7] systems. An assembly of colloidal particles at the interface exhibits distinct properties as opposed to their individual counterparts and changes the mechanical properties of the interface [8] itself. Gradual changes in such properties of colloidal particle and of the interface with the progression of assembly formation has created considerable interest.

Recent studies on ordered colloidal assemblies [9] is receiving attention due to the breadth of their applications [3,10–12]. It has been reported that thermo-optical tweezers can form continuous patterns of mesoscopic materials by heating a solid-liquid interface [13] which opens up a new path in lithography. Amino acids can be made to crystallize at the solution interface, which was successfully demonstrated for glycine in its supersaturated solution [14]. On the other hand techniques like heating the liquid-air interface using a focused laser also form assemblies using the fluid flows [15,16]. Dynamics of assembly formation and the effects on physical properties like surface charge, wettability, optical potential, and particle density were reported in Ref. [17]. However, the growth rate of the particle assembly and the heating efficiencies [18] in the above mentioned techniques involving optically induced direct-heating of the fluid are low.

In this manuscript, we present a study of the assembly formation of colloidal particles at air-water interface with assistance from an upconverting particle. Polystyrene particles of size 1 $\mu$m and microdiamonds of average diameter 500 nm with Nitrogen-Vacancy (NV) crystal defects were used as probe particles. We show that the assembly formation rate increases fourfold with much lesser laser power than direct heating of the surface with light. The effect of spectral overlap between UCP emission and NV absorption is also studied, and the results show that there is a definite non-radiative energy transfer from UCP to NV center assembly. It has to be noted that conventional non-radiative energy transfer is short-ranged [19] and the effect decays with distance as d$^{-6}$ and d$^{-4}$ for dipole-dipole and plane-dipole [20,21] interaction respectively. Our results ascertain that the microdiamonds are packed as close as 30 nm from the surface of UCP while forming the assembly. These findings of our investigation will provide more insights into assembly formation and the collective effects. Further, we anticipate that the efficient and accelerated assembling of colloidal particles will find applications in studying optical crystallization such as [22,23] and photoinduced assemblies [24,25]. Light scattering from the colloidal assemblies at the interface depends on the structure of the assembly and separation between the particles. In addition, it is possible to experiment with different structures [26,27] for light-guiding applications [28,29] by adjusting the geometry of the colloidal particles.

2. Theory

When excited with a 975 nm laser, the upconverting particle (UCP) undergoes a two-photon absorption process to emit visible light. However, the process of emission has a low efficiency of about 2-3 %. The rest of the energy is converted into heat [30,31]. The emission from such a particle placed near the top interface of a sessile water droplet forms a local hotspot. Due to the temperature rise at the particle, convection currents are generated which accumulate particles. A theoretical framework is implemented to explain the flow using COMSOL.

2.1 Numerical modeling of assisted self-assembly at air-water interface

To understand the flow behavior at the air-water interface due to the presence of a hot spot, we have performed numerical modeling in COMSOL Multiphysics [32,33] platform, through the laminar two-phase flow module to describe the fluid flow with the coupling of phase-field module for tracking the interface [34,35]. Heat transfer in fluid flow module is used to describe the heat distribution in the fluid flow and it is coupled with the laminar two-phase flow module. The flow is assumed to be laminar, incompressible, and the Boussinesq approximation is considered. The incompressible continuity equation is used for mass conservation, Navier-Stokes equation is for the conservation of momentum and the energy equation is for the conservation of energy. The governing equations are [32],

(1)$$\nabla \cdot\textbf{U} = {0}$$

(2)$$\frac{{\partial ({{\rho_0} \textbf{U}}})}{{\partial t}} + \nabla \cdot ({ {\rho_0} \textbf{U} \textbf{U}}) = \nabla \cdot[ P\textbf{I}+{\mu}(\nabla \textbf{U}+\nabla \textbf{U}^\textbf{T})] + {\rho_0}\textbf{g} - \frac{\rho_0(T - T_0)}{T_0}g+ \textbf{F}_{\textbf{s}}$$

(3)$$\frac{{\partial ({{\rho} {C_p} T}})}{{\partial t}} + \nabla \cdot ({ {\rho} {C_p} \textbf{U} T}) = \nabla \cdot[ k \nabla T] + {Q}$$

where, the fluid density at room temperature is $\rho _0$ ($kg/m^3$), dynamic viscosity of the fluid is $\mu$ ($Pa.s$), fluid pressure is $p$ ($Pa$), and the velocity of the fluid is $\textbf{U}$ ($m/s$). The gravitational constant is denoted by $\textbf{g}$ ($m/s^2$), and $I$ represents the identity matrix. The surface tension force is denoted by $\textbf{F}_{\textbf{s}}$ ($N/m^3$). The fluid temperature is denoted by $T$ ($K$), heat capacity at constant pressure is denoted by $C_p$ ($J/(kg-K)$), the thermal conductivity is denoted by $k$ ($W/(m.K)$) and the initial temperature is denoted by $T_0$ ($K$). The heating of the fluid due to viscous dissipation is denoted by $Q$. The temperature dependent parameters are fluid density $\rho = (\rho _0 + \Delta \rho )$, $\mu$, $C_p$ and $k$, with $\Delta \rho$ corresponding to the change in fluid density due to a change in temperature. The fluid density at room temperature $T_0$ and fluid dynamic viscosity $\mu$ varies across the air-water interface, and it is calculated as,

(4)$${\rho_0} = {\rho_1}{Z_{f,1}}+{\rho_2}{Z_{f,2}}$$

(5)$${\mu} = {\mu_1}{Z_{f,1}}+{\mu_2}{Z_{f,2}}$$

$\rho _2$ and $\mu _2$ denotes the density and dynamics viscosity of water medium respectively whereas, $\rho _1$ and $\mu _1$ denotes the density and dynamics viscosity of air medium, respectively. The fraction of the phase-field function $\phi$ is denoted by $Z_{f,1}$ and $Z_{f,2}$, and calculated as,

(6)$${Z_{f,1}} = \frac{1-\phi}{2}$$

(7)$${Z_{f,2}} = \frac{1+\phi}{2}$$

(8)$${Z_{f,1}}+{Z_{f,2}} = 1$$

the value of $\phi$ varies from $-1$ to $1$ across the interface. In air medium, the value of $\phi$ is $-1$, and the value of $\phi$ is $1$ for water medium. From Eqs. (4) and (5), in the water medium $\rho _0 = \rho _2$ ($\phi = 1$), and $\rho _0 = \rho _1$ ($\phi = -1$) in the air medium.

The phase-field method is a better choice for interface capturing in non-isothermal situations as the method takes care of the energy minimization of the system along with interface tracking. In this method, Cahn-Hilliard equation is solved to track the interface evolution. The method uses a phase-field variable $\phi$ to distinguish the air-water interface, and the governing equation for $\phi$ is [35],

(9)$$\frac{{\partial {\phi}}}{{\partial t}} + \nabla \cdot ({\phi \textbf{U}}) = \nabla \cdot \chi_1 \nabla{L}$$

where, the time scale of diffusion is denoted by $\chi _1$ ($m^3.s/kg$), and the chemical potential is represented by $L$, which is calculated as the rate of change of free energy $F$ at the interface ($L = \frac {\partial F}{\partial \phi }$). The free energy $F$ is [36]

(10)$${F(\phi,\nabla{\phi})} = \int \Bigg(\frac{1}{2}{\lambda}^2 {\mid \nabla \phi \mid}^2 + K_1(\phi) \Bigg) dV$$

where, the liquid-gas interface thickness is denoted by $\epsilon _{p}$ ($m$). The free energy has two components, one is inter-facial free energy density which is denoted by $\frac {1}{2}{\epsilon _{p}}^2 {\mid \nabla \phi \mid }^2$, and another is bulk energy density which is denoted by $K_1 = \frac {\lambda }{4{\epsilon _{p}}^2}(\phi ^2 -1)^2$ [36]. In the present work we have considered the Cahn number $Cn = \frac {\epsilon _{p}}{d_0}$ as $0.15$ [37]. The inter-facial energy $\sigma$ and the mixing energy density $\lambda$ ($N$) is related as, $\sigma = \frac {2\sqrt {2}}{3} \frac {\lambda }{\epsilon _{p}}$ [35]. The chemical potential $L$ is [36]

(11)$${L} = \frac{\partial F}{\partial \phi} = \lambda \Bigg( -\nabla^2 \phi + \frac{\phi (\phi^2-1)}{{\epsilon_{p}}^2} \Bigg)$$

In this work, to reduce the computational effort, we have decomposed the Cahn-Hilliard equation into two $2^{nd}$ order PDE as [32,35],

(12)$$\frac{{\partial ({\phi})}}{{\partial t}} +{\cdot}\nabla ({\phi} \textbf{U}) = \nabla \cdot \frac{\lambda \chi_1}{{\epsilon_{p}}^2} \nabla{\psi}$$

(13)$${\psi} ={-} \nabla \cdot {{\epsilon_{p}}^2} \nabla{\phi}+({{{\phi}^2}-1}) \phi + \Bigg(\frac{{\epsilon_{p}}^2}{\chi_1} \Bigg) \frac{\partial f}{\partial \phi}$$

The mobility $\chi _1$ is controlled by a parameter $\beta _1$ which is called a mobility tuning parameter. We have done the sensitivity study of $\beta _1$ and found $\beta _1 = 0.01$ $m.s/kg$ [38]. As in the present numerical model, there is no external supply of energy, thus the phi-derivative of the external free energy $\frac {\partial w}{\partial \phi }$ is taken as $0$. The surface tension force $\textbf{F}_{\textbf{s}}$ is calculated as [32]

(14)$$\textbf{F}_{\textbf{s}} = \Bigg ( \frac{\chi_1}{{\epsilon_{p}}^2} \psi - \frac{\partial w}{\partial \phi} \Bigg) \nabla \phi$$

We considered a 2D domain of width and height $10$ $mm$ each, with the bottom half of the domain being water and the top half to be air. We placed a solid ball of diameter $500$ $\mu m$ and temperature $40^{\circ }$ C at the center of the air-water interface, and it is assumed that the solid ball maintains this constant temperature throughout the fluid dynamics. To resemble the experimental situation, the solid ball works as a hot spot. The initial temperature of the air and water phase is considered to be $20^{\circ }$ C. Figure 1 shows the propagation of the heat into the water medium and the formation of the flow vortices. Due to the temperature gradient in the vicinity of the solid object, a surface tension force gradient at the air-water interface is developed, whereafter, vortices are developed near the vicinity of the hot spot.

Fig. 1. Development of the flow vortices near the hot spot, and the interfacial fluid flow velocity towards the hot spot. The legend corresponds the temperature contour in $K$. The black arrows are the resultant velocity vectors, and the red arrow denotes the overall direction of the developed vortices. The diameter of the solid ball ($500$ $\mu m$) corresponds the scale bar. The simulation indicates the early time development of the convection currents, in (a) to (c). In steady state, the convection currents stabilise to become like part (c).

Download Full Size | PDF

We would like to state here that the sense of convection currents remains the same even without the heating particle, when the focused laser beam is absorbed directly by water, but the velocity of the convection currents increases significantly with the presence of the particle. This is the reason that the particle assembly is accelerated significantly.

2.2 Non-radiative interaction

Here, we have used the thermal flows to form self-assemblies of 1 $\mu$m polystyrene and 500 nm microdiamonds with nitrogen-vacancy (NV) crystal defects. The microdiamonds bearing NV centers are fluorescent particles that absorb green light (532 nm) and emit red light (638 nm). Note that the emission from UCP (donor fluorophore) overlaps with the absorption wavelength of NV centers (acceptor fluorophore) in microdiamonds as shown in Fig. 2.

Fig. 2. A graph showing the spectral overlap (yellow) of emission spectrum (blue) from a single UCP, excited with 975 nm laser and absorption spectrum (red) of NV centers in microdiamonds.

Download Full Size | PDF

We probe whether there is a non-radiative energy transfer between the donor-acceptor fluorophore pair as follows.

\begin{array}{c} D~(Donor) + h\nu~(Incident~energy) \rightarrow D^{*} \\ D^{*} + A~(Acceptor) \rightarrow A^{*} \\ A^{*} \rightarrow A + h\nu^{\prime} \end{array}

where $D^{*}$, $A^{*}$ are the excited states of donor and acceptor fluorophores respectively and $\nu$, $\nu ^{\prime }$ are their corresponding emission frequencies. Energy transfer between the donor-acceptor pair is manifested through a decreased fluorescence from the donor and reduced lifetime of the excited donor [39]. This interaction is highly sensitive to the distance (d) between the D-A pair and is usually treated as a dipole-dipole interaction. The distance-dependent interaction varies as d$^{-6}$ for the dipole-dipole system and limits the interaction range to 10 nm. However, there are other configurations to enhance the energy transfer rate and increase the range of interaction. Specifically, when the NV dipole is placed close to a 2D surface (graphene monolayer), a Forrester Resonance Energy Transfer (FRET) efficiency ($\eta$) of 40$\%$ is realized as demonstrated in the Ref. [21]. The distance-dependence of energy transfer here varies as d$^{-4}$ extending the interaction range up to 30 nm. Another configuration where a single dipole (donor) interacts with multiple dipoles (10 acceptors) at a distance (R $\approx$ 20 nm) also shows an increased energy transfer rate [40]. It is assumed that the distance between two acceptors (r$_i$) is negligible compared to the distance from the donor (R).

3. Materials and methods

3.1 Experimental procedure

The setup used for the experiment is as depicted in Fig. 3.

Fig. 3. (a) Schematic of the experimental setup showing various components and laser beam path along with an inset of optical trap at the air-water interface of the sessile water droplet.

Download Full Size | PDF

It is designed by altering the optical tweezers kit (Thorlabs, OTKB/M). A 100x (1.3 numerical aperture) oil immersion objective from Olympus is placed in an inverted microscope configuration for simultaneous imaging and trapping. A diode laser of wavelength 975 nm from Thorlabs is linearly polarised using a polarizing beam splitter and reflected by a dichroic mirror towards the 100x objective. The laser beam is focused onto the sample plane where a 3 $\mu$L sessile water droplet with suspended UCPs and colloidal particles is placed on a coverslip (English glass, Blue star, number 1 size) and clipped to the sample stage. Further, the sample stage is illuminated by a white light LED source coupled into the laser beam path with a dichroic mirror and a condenser objective lens (10x, 0.25 air-immersion, Nikon) as shown in Fig. 3. In addition, the combination of an objective lens and dichroic mirror directs the visible light towards a 50-50 beam splitter. A CMOS camera is placed at an output port of the beam splitter to image the sample plane. The other output port is used to either collect the emission spectrum from the particle or to measure the lifetime of an excited state in accordance with the experiment.

3.2 Sample preparation

Conventional hydrothermal method [41] is used to synthesize the Iron doped upconverting hexagonal particles (Fe-NaYF$_4$: Er, Yb) with required modification as described in [42]. Iron (Fe) doping can be varied from 5 - 30 $\%$. However, for all our experiments we have used 15 $\%$ Fe doped UCPs. Preparation of Fe-doped UCPs requires a 14 mL aqueous solution with 1.014 g of Yttrium nitrate (Y(No$_3$)$_3$) and 1.23 g of trisodium citrate mixed vigorously with a magnetic stirrer for 10 minutes. Similarly, another aqueous solution is prepared by adding 0.259 g of Iron nitrate (Fe(No$_3$)$_3$), 0.38 g of Ytterbium nitrate (Yb(No$_3$)$_3$) and 0.037 g of Erbium nitrate (Er(No$_3$)$_3$) to 21 mL distilled water. The above two solutions when mixed together turn into a milky white solution. Further, a 67 mL, 0.5 M NaF aqueous solution is added to the milky white solution and stirred for 60 minutes to obtain a transparent solution. The transparent solution is then transferred to a Teflon-lined autoclave (200 mL) and heated in a muffle furnace for 12 hours at 200 $^{\circ }$C. Consequently, it has to be cooled down to room temperature and the iron-doped UCPs are settled at the bottom. Then, the solution is washed with distilled water and ethanol multiple times. The powdered sample is collected by drying the solution at 100 $^{\circ }$C. Polystyrene particles of diameter 1 $\mu$m (Sigma-Aldrich, 69057-5ML-F) and microdiamonds (Adamas Nanotechnologies, MDNV1umHi10mg) with NV crystal defects of average size of 500 nm were used in the experiment as probes.

4. Results and discussions

The low emission efficiency of UCP tends to heat up the surrounding medium which is dissipated into surroundings through various mechanisms. However, the heating effects are more prominent at the interface as the heat dissipation is not uniform in all directions. Vapor bubbles are formed when the UCP is placed near the interface of a sessile water droplet [43] and irradiated with 975 nm laser of 20 mW power. Hence, close to the side interface the temperature is expected to be close to the boiling point of water (100$^{\circ }$ C). In our experiments, we have used a laser power of about 10 mW which corresponds to a temperature of about 40$^{\circ }$ C at the interface. The flow patterns obtained from the simulations assuming a temperature of 40$^{\circ }$ C are in good agreement with our experimental observations.

4.1 Accelerated self-assembly of colloidal particles

It has been demonstrated that temperature gradient due to local heating in fluids can be used to create and efficiently control the fluid flows. The effects of temperature gradient are stronger near the interface than in bulk. Here, a single UCP is placed at the air-water interface of a sessile water droplet to heat its surrounding thereby generating fluid flow. Consequently, suspended colloidal particles are pulled towards the hot spot from the bulk to the surface.

We show that the polystyrene particle suspensions in a sessile water droplet of size 1 $\mu$m aggregates around the trapped UCP near the interface. These aggregates of polystyrene particles expand uniformly around the UCP in a hexagonal arrangement as depicted in the sequence of images in Fig. 4(a) - (g). The evolution of the aggregate size is characterized by measuring the radius (R) in $\mu$m of the assembly as a function of laser irradiation time (T) in seconds. A straight line is fitted to the plot as shown in Fig. 5 to estimate the growth rate which is about 0.35 $\mu$m/s. In our system, a laser of power about 10 mW is irradiated for 30 s at the interface to form aggregates of size 15 $\mu$m. However, in the absence of UCP, laser power as high as 100 mW irradiated for 30 s is required to form an aggregate of size about 4 $\mu$m as demonstrated in Ref. [17]. Hence, a tenfold decrease in laser power and a fourfold increase in aggregate size are achieved with our system. Enhanced heating of the interface by UCP is evident from these observations.

Fig. 4. (a) An image of a single upconverting particle (UCP) trapped at the air-water interface and excited with 975 nm laser emitting visible light and locally heating the interface at t = 0 s. A series of snapshots (b) - (g) depicting the evolution of the size of hexagonal close-packed assembly of suspended 1 $\mu$m polystyrene particles at later times.

Download Full Size | PDF

Fig. 5. A graph showing the radius of the assembly as a function of laser irradiation time fitted to a straight line (red) with slope (an estimate of the growth rate) 0.35 $\mu$m/s.

Download Full Size | PDF

4.2 Self-assembly of microdiamonds: demonstration of long-range FRET

Diamonds intrinsically have a high refractive index which makes them difficult to confine in 3D (dimensions) using optical tweezers. Instead, they are confined in 2D by an optical potential and pushed towards a surface to form a pseudo 3D trap [44]. In addition, these particles are inert and have to be very closely packed to perceive interactions between them. It is here, we show that the self-assembly of microdiamonds is a close-packed lattice-like structure formed within 30 nm from the surface of the UCP using FRET measurement.

In order to demonstrate long-range FRET we consider a system with microdiamonds bearing NV center crystal defects and a single UCP. These microdiamonds act as acceptors which are aggregated around a donor fluorophore (UCP) tracing the fluid flows at the air-water interface as depicted in Fig. 6(a).

Fig. 6. A snapshot of (a) an assembly of microdiamonds aggregated around a single UCP at the air-water interface when the 975 nm laser is turned off. (b) An image depicting the emission from UCP when the laser is irradiated. The diamond particles are still assembled around the UCP but cannot be seen in the image due to the brightness of the emission from UCP. (c) A graph showing the green emission lifetime fitted to an exponential decay function of a single UCP in presence (red) and absence (blue) of NV acceptors assembly.

Download Full Size | PDF

The emission of UCP has three bands blue, green, and red with wavelength ranges of 460 - 470, 520 - 560, and 640 - 670 nm respectively. Further, the microdiamonds with NV center crystal defects have broad absorption between 520 - 570 nm overlapping with the emission spectrum.

As discussed in section 2.2 the non-radiative energy transfer rate between the acceptor-donor pair can be manifested as the change in lifetime of the excited donor ($D^{*}$). Here, we employ Time-Correlated Single Photon Counting (TCSPC) technique to measure the fluorescence lifetime of our samples. The green emission from UCP is collected using a band-pass filter with a wavelength range of 550 $\pm$ 10 nm. Lifetime ($\tau$) of the filtered green emission from an isolated UCP is about 100 $\mu$s and is observed to reduce to 64 $\mu$s in presence of the NV center acceptors as shown in Fig. 6(c). This reduced lifetime of green emission emphasizes the non-radiative energy transfer between the trapped donor UCP and the aggregated NV acceptors around the UCP. Furthermore, we have observed that the red emission (long-pass filter, 575 nm) lifetime is not affected in presence of NV center acceptors and the lifetime is about 58 $\pm$ 2 $\mu$s. Note that there is no spectral overlap for wavelengths above 575 nm. Hence, the non-radiative energy transfer between UCP and NV centers happens only in the green emission range (520 - 560 nm).

We have built statistics for green and red emission lifetimes from UCP as shown in Fig. 7(a) and (b) respectively. The analysis is performed with about 20 lifetime measurements of green emission and 10 measurements of red emission each in presence and absence of aggregated microdiamonds with NV acceptors. We estimate the mean lifetime for green (red) emission in presence of NV acceptors to be 55 $\pm$ 5 $\mu$s (60 $\pm$ 2.5 $\mu$s) and in their absence, the mean lifetime is 93 $\pm$ 8 $\mu$s (55.6 $\pm$ 2.7 $\mu$s). In addition, a paired t-test analysis on the data sets (with and without NV acceptors) for green and red emission lifetimes has p values of 0.0001 and 0.127 respectively. Hence, the green emission lifetime is significantly changed in presence of NV acceptors. On the other hand, the change in red emission lifetime is not statistically significant.

Fig. 7. Scatter plots depicting the mean lifetimes of (a) green and (b) red emissions from UCP in presence (red markers) and in absence (blue markers) of an assembly of NV acceptors formed using optically assisted heating of air-water interface.

Download Full Size | PDF

In our system, the assembly of microdiamonds bearing NV centers is close to the surface of a UCP at an air-water interface. The concentration of NV centers per particle of size 500 nm is 3 ppm which translates to 37$\times 10^3$ centers. We estimate there are 300 - 400 acceptors in the vicinity of 30 nm from the donor considering they are uniformly distributed across the particle. Further, FRET efficiency ($\eta$) is calculated from Eq. (15).

(15)$$\eta = 1 - \frac{\tau_a}{\tau_i}$$

where $\tau _i$ and $\tau _a$ are the lifetimes of the UCP (donor) when isolated and in presence of an assembly of acceptors respectively. A FRET efficiency of 40% is obtained for green emission calculated using Eq. (15). We do not believe that the assembly formed underneath the UCP is actually a periodic lattice since the diamonds are irregular in shape (in contrary to spherically shaped polystyrene). Thus, we do not have a photonic crystal. The interaction between the emission from the UCP and the diamonds can only be through the NV centers.

This technique can be further investigated to ascertain whether the birefringence axes of the diamonds could be made to align while forming the self-assembly. Then, the NV axes may also align whereafter this assembly might exhibit collective radiative features in NV emission [45,46], an interesting topic of current research [47,48]. The present work is a step in that direction.

We would also like to state that there is no difference between the UCP and any other absorbing particle towards the formation of the self-assembly. This optically trapped and heated particle only acts to generate heat, which in turn causes the formation of the convection currents to bring other particles for the assembly. However, UCP has a conducive refractive index of about 1.55 which allows it to be easily optically confined. Particles of materials like Haematite which have high refractive index are very difficult to be optically trapped in three dimensions, since the scattering force becomes larger than the gradient force.

5. Conclusion

Thus, in conclusion, we show that higher temperatures are obtained by placing a UCP at the air-water interface and illuminating it with a 975 nm laser beam. This generates stronger convection currents in the fluid than direct illumination of the surface with the laser, thereby generating an assembly much faster. We also show that these convection currents create a lattice-like assembly on the interface as well as under the UCP. Usage of microdiamonds exhibits the presence of the NV centers, and hence diamonds, well within the 30 nm distance required to cause non-radiative energy transfer from the UCP to the NV centers. The lifetime of the 550 nm emission from the UCP reduces from about 90 $\mu$s to about 50 $\mu$s in the presence of the self-assembly of the diamonds. Further detailed studies are required to ascertain the sensitivity of this non-radiative energy transfer to external stimuli like magnetic fields and the effects of aligned self-assembly of microdiamonds.

Funding

Department of Science and Technology, Ministry of Science and Technology, India (DST/ICPS/QuST/Theme-2/2019/General); Department of Biotechnology, Ministry of Science and Technology, India (IA/I/20/1/504900).

Disclosures

The authors declare that there are no conflicts of interest.

Data availability

The data for the manuscript are available upon reasonable request to authors.

References

1. E. Jaquay, L. J. Martínez, C. A. Mejia, and M. L. Povinelli, “Light-assisted, templated self-assembly using a photonic-crystal slab,” Nano Lett. 13(5), 2290–2294 (2013). [CrossRef]

2. B.-W. Li, M.-C. Zhong, and F. Ji, “Laser induced aggregation of light absorbing particles by marangoni convection,” Appl. Sci. 10(21), 7795 (2020). [CrossRef]

3. K.-i. Yuyama, M. Ueda, S. Nagao, S. Hirota, T. Sugiyama, and H. Masuhara, “A single spherical assembly of protein amyloid fibrils formed by laser trapping,” Angew. Chem. Int. Ed. 56(24), 6739–6743 (2017). [CrossRef]

4. M. Zhong, Z. Wang, and Y. Li, “Laser-accelerated self-assembly of colloidal particles at the water–air interface,” Chin. Opt. Lett. 15(5), 051401 (2017). [CrossRef]

5. R. McGorty, J. Fung, D. Kaz, and V. N. Manoharan, “Colloidal self-assembly at an interface,” Mater. Today 13(6), 34–42 (2010). [CrossRef]

6. K. V. Kinhal, S. Sinha, A. Ravisankar, N. P. Bhatt, and S. Pushpavanam, “Simultaneous synthesis and separation of nanoparticles using aqueous two-phase systems,” ACS Sustainable Chem. Eng. 8(7), 3013–3025 (2020). [CrossRef]

7. B. P. Binks, “Colloidal particles at a range of fluid–fluid interfaces,” Langmuir 33(28), 6947–6963 (2017). [CrossRef]

8. M. Jose, M. Lokesh, R. Vaippully, D. K. Satapathy, and B. Roy, “Temporal evolution of viscoelasticity of soft colloid laden air–water interface: a multiple mode microrheology study,” RSC Adv. 12(21), 12988–12996 (2022). [CrossRef]

9. I. Aibara, C.-H. Huang, T. Kudo, R. Bresoli-Obach, J. Hofkens, A. Furube, and H. Masuhara, “Dynamic coupling of optically evolved assembling and swarming of gold nanoparticles with photothermal local phase separation of polymer solution,” J. Phys. Chem. C 124(30), 16604–16615 (2020). [CrossRef]

10. T. Kudo, S.-F. Wang, K.-i. Yuyama, and H. Masuhara, “Optical trapping-formed colloidal assembly with horns extended to the outside of a focus through light propagation,” Nano Lett. 16(5), 3058–3062 (2016). [CrossRef]

11. R. Bresolí-Obach, S. Nonell, H. Masuhara, and J. Hofkens, “Chemical control over optical trapping force at an interface,” Adv. Opt. Mater. 10(17), 2200940 (2022). [CrossRef]

12. Y.-C. Chang, R. Bresolí-Obach, T. Kudo, J. Hofkens, S. Toyouchi, and H. Masuhara, “The optical absorption force allows controlling colloidal assembly morphology at an interface,” Adv. Opt. Mater. 10(13), 2200231 (2022). [CrossRef]

13. B. Roy, M. Arya, P. Thomas, J. K. Jurgschat, K. Venkata Rao, A. Banerjee, C. Malla Reddy, and S. Roy, “Self-assembly of mesoscopic materials to form controlled and continuous patterns by thermo-optically manipulated laser induced microbubbles,” Langmuir 29(47), 14733–14742 (2013). [CrossRef]

14. T. Sugiyama and H. Masuhara, “Laser-induced crystallization and crystal growth,” Chem. Asian J. 6(11), 2878–2889 (2011). [CrossRef]

15. C.-L. Wu, S.-F. Wang, T. Kudo, K.-i. Yuyama, T. Sugiyama, and H. Masuhara, “Anomalously large assembly formation of polystyrene nanoparticles by optical trapping at the solution surface,” Langmuir 36(47), 14234–14242 (2020). [CrossRef]

16. S.-F. Wang, T. Kudo, K.-i. Yuyama, T. Sugiyama, and H. Masuhara, “Optically evolved assembly formation in laser trapping of polystyrene nanoparticles at solution surface,” Langmuir 32(47), 12488–12496 (2016). [CrossRef]

17. S. Pradhan, C. P. Whitby, M. A. Williams, J. L. Chen, and E. Avci, “Interfacial colloidal assembly guided by optical tweezers and tuned via surface charge,” J. Colloid Interface Sci. 621, 101–109 (2022). [CrossRef]

18. E. J. Peterman, F. Gittes, and C. F. Schmidt, “Laser-induced heating in optical traps,” Biophys. J. 84(2), 1308–1316 (2003). [CrossRef]

19. H. Fujiwara, K. Sasaki, and H. Masuhara, “Enhancement of förster energy transfer within a microspherical cavity,” ChemPhysChem 6(11), 2410–2416 (2005). [CrossRef]

20. K. Yuan, Y. Liu, Z. Ou-Yang, J. Liu, Y. Yang, and J. Sun, “Resonant energy transfer between rare earth atomic layers in nanolaminate films,” Opt. Lett. 47(19), 4897–4900 (2022). [CrossRef]

21. X. Liu, G. Wang, X. Song, F. Feng, W. Zhu, L. Lou, J. Wang, H. Wang, and P. Bao, “Energy transfer from a single nitrogen-vacancy center in nanodiamond to a graphene monolayer,” Appl. Phys. Lett. 101(23), 233112 (2012). [CrossRef]

22. K.-i. Yuyama, T. Sugiyama, and H. Masuhara, “Laser trapping and crystallization dynamics of l-phenylalanine at solution surface,” J. Phys. Chem. Lett. 4(15), 2436–2440 (2013). [CrossRef]

23. M. M. Burns, J.-M. Fournier, and J. A. Golovchenko, “Optical matter: crystallization and binding in intense optical fields,” Science 249(4970), 749–754 (1990). [CrossRef]

24. T. Shoji, M. Shibata, N. Kitamura, F. Nagasawa, M. Takase, K. Murakoshi, A. Nobuhiro, Y. Mizumoto, H. Ishihara, and Y. Tsuboi, “Reversible photoinduced formation and manipulation of a two-dimensional closely packed assembly of polystyrene nanospheres on a metallic nanostructure,” J. Phys. Chem. C 117(6), 2500–2506 (2013). [CrossRef]

25. K.-Y. Chen, A.-T. Lee, C.-C. Hung, J.-S. Huang, and Y.-T. Yang, “Transport and trapping in two-dimensional nanoscale plasmonic optical lattice,” Nano Lett. 13(9), 4118–4122 (2013). [CrossRef]

26. J.-S. Lu, T. Kudo, B. Louis, R. Bresolí-Obach, I. G. Scheblykin, J. Hofkens, and H. Masuhara, “Optical force-induced dynamics of assembling, rearrangement, and three-dimensional pistol-like ejection of microparticles at the solution surface,” J. Phys. Chem. C 124(49), 27107–27117 (2020). [CrossRef]

27. X. Chen, W. Cheng, M. Xie, and F. Zhao, “Optical rotational self-assembly at air-water surface by a single vortex beam,” Results Phys. 12, 1172–1176 (2019). [CrossRef]

28. R. M. Bakker, Y. F. Yu, R. Paniagua-Domínguez, B. Luk’yanchuk, and A. I. Kuznetsov, “Resonant light guiding along a chain of silicon nanoparticles,” Nano Lett. 17(6), 3458–3464 (2017). [CrossRef]

29. W. Ahn, X. Zhao, Y. Hong, and B. M. Reinhard, “Low-power light guiding and localization in optoplasmonic chains obtained by directed self-assembly,” Sci. Rep. 6(1), 22621 (2016). [CrossRef]

30. I. V. Krylov, R. A. Akasov, V. V. Rocheva, N. V. Sholina, D. A. Khochenkov, A. V. Nechaev, N. V. Melnikova, A. A. Dmitriev, A. V. Ivanov, A. N. Generalova, and E. V. Khaydukov, “Local overheating of biotissue labeled with upconversion nanoparticles under yb3+ resonance excitation,” Front. Chem. 8, 295 (2020). [CrossRef]

31. A. D. Pickel, A. Teitelboim, E. M. Chan, N. J. Borys, P. J. Schuck, and C. Dames, “Apparent self-heating of individual upconverting nanoparticle thermometers,” Nat. Commun. 9(1), 4907 (2018). [CrossRef]

32. C. Multiphysics, “Comsol multiphysics cfd module user guide (version 5.3 a),” COMSOL pp. 208–265 (2015).

33. I. U. Chowdhury, P. S. Mahapatra, and A. K. Sen, “A wettability pattern-mediated trapped bubble removal from a horizontal liquid–liquid interface,” Phys. Fluids 34(4), 042109 (2022). [CrossRef]

34. X. Cai, H. Marschall, M. Wörner, and O. Deutschmann, “Numerical simulation of wetting phenomena with a phase-field method using openfoam®,” Chem. Eng. Technol. 38(11), 1985–1992 (2015). [CrossRef]

35. F. Bai, X. He, X. Yang, R. Zhou, and C. Wang, “Three dimensional phase-field investigation of droplet formation in microfluidic flow focusing devices with experimental validation,” Int. J. Multiphase Flow 93, 130–141 (2017). [CrossRef]

36. H. Liu and Y. Zhang, “Droplet formation in a t-shaped microfluidic junction,” J. Appl. Phys. 106(3), 034906 (2009). [CrossRef]

37. Y. Wu, F. Wang, M. Selzer, and B. Nestler, “Investigation of equilibrium droplet shapes on chemically striped patterned surfaces using phase-field method,” Langmuir 35, 8500–8516 (2019). [CrossRef]

38. I. U. Chowdhury, P. S. Mahapatra, A. K. Sen, A. Pattamatta, and M. K. Tiwari, “Autonomous transport and splitting of a droplet on an open surface,” Phys. Rev. Fluids 6(9), 094003 (2021). [CrossRef]

39. T. Riuttamaki, I. Hyppanen, J. Kankare, and T. Soukka, “Decrease in luminescence lifetime indicating nonradiative energy transfer from upconverting phosphors to fluorescent acceptors in aqueous suspensions,” J. Phys. Chem. C 115(36), 17736–17742 (2011). [CrossRef]

40. P. Bojarski, L. Kulak, K. Walczewska-Szewc, A. Synak, V. M. Marzullo, A. Luini, and S. D’Auria, “Long-distance fret analysis: a monte carlo simulation study,” J. Phys. Chem. B 115(33), 10120–10125 (2011). [CrossRef]

41. M. Lokesh, G. Nalupurackal, S. Roy, S. Chakraborty, J. Goswami, M. Gunaseelan, and B. Roy, “Generation of partial roll rotation in a hexagonal nayf 4 particle by switching between different optical trapping configurations,” Opt. Express 30(16), 28325–28334 (2022). [CrossRef]

42. G. Nalupurackal, G. M M. Lokesh, R. Vaippully, A. Chauhan, B. R. K. Nanda, C. Sudakar, H. C. Kotamarthi, A. Jannasch, E. Schffer, J. Senthilselvan, and B. Roy, “Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom,” (2022).

43. S. Kumar, A. Kumar, M. Gunaseelan, R. Vaippully, D. Chakraborty, J. Senthilselvan, and B. Roy, “Trapped in out-of-equilibrium stationary state: hot brownian motion in optically trapped upconverting nanoparticles,” Front. Phys. 8, 570842 (2020). [CrossRef]

44. M. Lokesh, R. Vaippully, G. Nalupurackal, S. Roy, V. P. Bhallamudi, A. Prabhakar, and B. Roy, “Estimation of rolling work of adhesion at the nanoscale with soft probing using optical tweezers,” RSC Adv. 11(55), 34636–34642 (2021). [CrossRef]

45. C. Bradac, M. T. Johnsson, M. v. Breugel, B. Q. Baragiola, R. Martin, M. L. Juan, G. K. Brennen, and T. Volz, “Room-temperature spontaneous superradiance from single diamond nanocrystals,” Nat. Commun. 8(1), 1205 (2017). [CrossRef]

46. J. Gutsche, A. Zand, M. Bültel, and A. Widera, “Revealing superradiant emission in the single-to-bulk transition of quantum emitters in nanodiamond agglomerates,” New J. Phys. 24(5), 053039 (2022). [CrossRef]

47. P. Solano, P. Barberis-Blostein, F. K. Fatemi, L. A. Orozco, and S. L. Rolston, “Super-radiance reveals infinite-range dipole interactions through a nanofiber,” Nat. Commun. 8(1), 1857 (2017). [CrossRef]

48. A. Karnieli, N. Rivera, A. Arie, and I. Kaminer, “Superradiance and subradiance due to quantum interference of entangled free electrons,” Phys. Rev. Lett. 127(6), 060403 (2021). [CrossRef]

Accelerated self assembly of particles at the air-water interface with optically assisted heating due to an upconverting particle

Abstract

1. Introduction

2. Theory

2.1 Numerical modeling of assisted self-assembly at air-water interface

2.2 Non-radiative interaction

3. Materials and methods

3.1 Experimental procedure

3.2 Sample preparation

4. Results and discussions

4.1 Accelerated self-assembly of colloidal particles

4.2 Self-assembly of microdiamonds: demonstration of long-range FRET

5. Conclusion

Funding

Disclosures

Data availability

References

Data availability

Cited By

Figures (7)

Equations (16)

Optics Express