Fig. 1. The lock-in imager sensor. Panel A shows microphotography of the sensor. Each single pixel, arranged in a 124×160 array has a dimension of about 40μm × 55μm. Each pixel has two gates that are controlled with voltages in opposite phase (Panel B). Thus, the photoelectrons generated in the photosensitive area, will accumulate in the two storage areas according to the relative phase of the photon flux and the gate potentials.

Fig. 2. Response of the lock-in imager. Panel A and B show the average intensity at each detected phase. The grey curve represents the average intensity (I₀) and the circles are the experimental points connected by a spline curve (dashed). Gray circles correspond to images acquired by the injection of the additional delay by the external delay unit. The left side panels (A, C and E) represent measurements of a reflective foil, while B, D and F refer to a fluorescent slide acquisition. C and D depict the demodulation of the signal measured over the entire illuminated field of view; E and F show the correspondent phases. The latter are inhomogeneous over the field of view (arrows). Considering the lifetime of the samples, i.e. 0 ns and 4.8 ns for the reflective foil and fluorescent slide, respectively, the initial phase of the detection is shown to be constant, while the demodulations suffer from a color-effect of the lock-in imager.

Fig. 3. Fluorescence lifetime sensing. The lock-in imager distinguishes compounds with different fluorescent lifetimes. Panel A shows the phase-lifetime maps and distributions of: EGFP in solution (gray line), a fluorescent slide (dashed curve) and DNA-bound GelStar (black solid line) in solution. The lifetimes were 2.6±0.4 ns, 4.8±0.4 ns and 6.6±0.7 ns, respectively. Both the phase- (panel B, gray curve) and demodulation- (black line) lifetimes can be measured at a modulation frequency of 20MHz. A Turbo-Sapphire GFP bead showed values of 2.67±0.09 ns and 3.7±0.2 ns, respectively. Panel B inset (R6G) shows the phase (4.3±0.2) and modulation (4.3±0.4) lifetime of the mono-exponential decaying fluorophore standard Rhodamine 6G.