Fig. 2: Single measurement of fluorescent nanospheres with the SPAD array detector.
From: Single-photon microscopy to study biomolecular condensates
a FCS measurement of fluorescent nanospheres in water. The three curves correspond to the three volumes considered with the SPAD array detector. The three autocorrelation curves are fitted with a model for one diffusing component (black lines). b Spot-variation FCS measurement of fluorescent nanospheres in water. The diffusing times are calculated from the autocorrelation curves shown in (a). Here, the diffusion law confirms a free motion with an intercept value of −0.03 ± 0.03 ms and a diffusion coefficient of 17.7 ± 0.3 μm2 s−1, which corresponds to a diameter of 24 nm (20 nm from the manufacturing). c Histogram of the fluorescence decay calculated from the same dataset used in (a). A histogram of the fluorescence decay is calculated for each of the 25 channels of the SPAD array detector. The black line represents the data from the central detector channel. The fluorescence lifetime value can be retrieved by fitting the data with an exponential function (τF = 1.3 ± 0.1 ns). d, e Cross-correlation experiment with fluorescent nanospheres. A mix of beads with two colors is used for the measurements (yellow-green and red). The SPAD array detector is equipped with a filter for green fluorescence signals, while the single-element detector has a filter for red fluorescence signals. While the signal is autocorrelated in every detector alone (only the Sum 3 × 3 is shown here for the SPAD array detector), the cross-correlation shows a low amplitude, suggesting low interaction between the two samples. f, g Only yellow-green fluorescent nanospheres are diluted in water and measured. The signal is split equally on the two detector arms equipped with the same detection filter. The intensity time trace can be well-correlated in both detectors (only the Sum 3 × 3 is shown here for the SPAD array detector). As expected here, the cross-correlation curve has a high amplitude as the signal is the same for both detectors. Source data are provided as a Source Data file and raw files.
