L-lysine biodetector based on a TOCNFs-coated Quartz Crystal Microbalance (QCM)

Developing a simple, cost effective and accurate detection method for L-lysine (Lys), L-leucine (Leu) and glycine (Gly) as the important analytes in clinical diagnostics, biological processes and food industries is of great significance. Herein, we prepared spin-coated TEMPO-oxidized cellulose nanofibrils (TOCNFs) on Quartz Crystal Microbalance (QCM) chip to achieve QCM biodetectors. The coated QCMs were carefully characterized before and after interaction with amino acids (AA) using water contact angle (WCA), Fourier transform infrared spectrophotometry-attenuated total reflectance (FTIR-ATR), Raman spectroscopy, and scanning electron microscopy (SEM). In addition, to study the response of the fully covered QCM chips to the aqueous AA, the frequency reductions of the detectors in proportion to different AA concentrations (10-1000 mu g/mL) were recorded. The data showed a linear range of detection R2 = 0.9987, 0.9933, 0.9833 and a calculated limit of detection (LOD) equal to 49, 113 and 178 mu g/ml for Lys, Gly and Leu, respectively. We observed the highest frequency shifts (the strongest interaction with TOCNFs) for Lys detection while response to Leu was negligible.