To assess sensitivity, we calculated the SNR by referencing the SWCNT signal ISWCNT to the background signal IB without SWCNTs (Figure ). Although the photocurrent density was approximately 60 % higher for the InGaAs PIN photodiode at all SWCNT surface chemistries, the SNR showed a 20 % higher value for the Si PIN photodiode (Figure ). For the Si PIN photodiode, all SWCNT surface chemistries reach an SNR greater than 1 for concentrations above 0.35 nM. Since the fluorescence intensity of the SWCNT depends on their surface chemistry the slopes differ. Overall, these results indicate that a lower SWCNT concentration may suffice for effective sensing with Si SIN photodiodes compared to InGaAs SIN photodiodes. ), Experimental Section) was fitted to the data points (fit parameters: Si: Kd = 0.9 µM ± 0.4 µM, A = 0.32 ± 0.03, and B = 0.05 ± 0.02; InGaAs: Kd = 0.7 µM ± 0.3 µM, A = 0.32 ± 0.02, and B = 0.04 ± 0.02). All data = mean ± SD, n = 3.