Lock-In Pixel CMOS Image Sensor for Time-Resolved Fluorescence Readout of Lateral-Flow Assays

We present a CMOS image sensor (CIS) based time-resolved fluorescence (TRF) measurement system for filter-less, highly sensitive readout of lateral-flow assay (LFA) test strips. The CIS contains a 256 × 128 lock-in pixel (LIP) sensor array. Each pixel has a size of $10 \ {\mu }\mathrm{m}$ × $10 \ {\mu }\mathrm{m}$ and includes a photodiode acting as signal transducer. The LIP CIS was designed in a standard 0.18 ${\mu }$$\mathrm{m}$ CMOS technology specifically for TRF applications. The LIP architecture blocks interfering light when fluorophores are excited and accumulates the emitted fluorescence light to be measured over multiple cycles after excitation. This allows to detect even small amounts of fluorescence light over a wide analyte concentration range. The LIP CIS based TRF reader was characterized in terms of reproducible and uniform signal intensities with use of appropriate Europium(III) [Eu 3+] chelate particles as fluorescence standards. We measured different concentrations of Eu-based nanoparticles (NP) on test strips with the TRF reader. The sensor system shows 5.1 orders of magnitude of detection dynamic range (DDR) with a limit of detection (LoD) of $0.1 \ \text{ng/cm}$. In addition, using human C-reactive protein (hCRP) as a model analyte, we compared the developed TRF reader with a commercial colorimetric LFA reader. For the quantification of CRP, the LIP CIS based TRF reader demonstrates a DDR of 3.6 orders of magnitude with an excellent LoD of $0.05 \ \text{ng/mL}$, which is 14 times better than the LoD of the commercial LFA reader.