Fig. 2: CreDiT system engineering.

a CreDiT approach to fluorescent detection. The digital input, represented by a Walsh–Hadamard (WH) sequency, is transformed into a fluorescent excitation waveform using a fast WH transform (FWHT). The resulting signal from a sample is processed via inverse FWHT (iFWHT) to recover WH sequency, whose amplitude is proportional to the fluorescent intensity. b Digital CreDiT detection outperformed analog lock-in (Fourier) and direct fluorescent detection, exhibiting a higher signal-to-noise ratio (SNR) than the others. Data were displayed as mean intensity ± s.d. from technical replicates (n = 10). c Samples with varying fluorescein concentrations were measured. With its high SNR, digital CreDiT detection achieved >2200-fold lower detection limit (0.4 pM) than the analog lock-in method (Fourier; 1 nM). Data were displayed as mean ± s.d. from triplicate measurements. d The digital CreDiT results from (c) also showed an excellent correlation (R² = 0.99) with those measured by a conventional plate reader. e Sample heating setup. The sample holder accommodated 12 samples for heating and was embedded with four pairs of a heater and a temperature sensor. An external fan was used to expedite sample cooling. f Sample temperature profile. The system reached different temperature targets for the CreDiT assay (e.g., NA extraction, CreDiT reaction). Thermal imaging (inset) confirmed uniform heating of all 12 samples. g The heating system maintained the target temperature with relative variations <0.6%. Data were shown as mean ± s.d. from repeated temperature measurements (n = 100). a.u. arbitrary unit. Source data are provided as a Source Data file.