Figure 2. PCBAA surface modification enabling SERS detection in undiluted human blood plasma.

(a) SERS spectra acquired with the unmodified SERS optofluidic system. From top to bottom, spectra shown were recorded after flowing undiluted plasma, PBS and plasma spiked with 1 μM R6G each for 10 min. (b) SERS spectra acquired with the pCBAA-modified SERS optofluidic system. From top to bottom, spectra shown were recorded after flowing PBS, undiluted plasma and plasma containing 1 μM R6G each for 10 min, along with the subtracted spectrum from the last two. λ_ex=785 nm, P_laser=1 mW and t=30 s with three accumulations. (c) Monitoring plasma protein adsorption and detecting R6G in plasma with the unmodified and pCBAA-modified SERS optofluidic system. Peak intensity of the amide I at 1,649 cm⁻¹ for protein and the C–C stretching at 1,508 cm⁻¹ for R6G were recorded as a function of time as PBS, plasma, PBS and R6G-spiked plasma were flowed sequentially. (d) Typical SPR sensorgram of protein adsorption from undiluted plasma on a bare gold and pCBAA-modified gold surface, showing protein adsorption of 452 and 0.3 ng cm⁻², respectively.