Highly Selective and Label-Free AuNPs Based Optical Sensor Development Significant in Smartphone Sensing of L-Lactate in Food Samples

Abstract

L-lactate is an essential organic chemical in food processing, clinical, chemical, and fermentation industries. AuNPs were synthesized by chemical reduction reaction method and functionalized with 3-aminophenylboronic acid (3-APBA). The structural, morphological, FTIR, DLS, zeta potential characterization studies were performed to optimize the sensing mechanism. First time reporting facile enzyme-free sensor for the detection of L-lactate content in milk. Initially, the sensor has been optimized for nano reagent concentration, pH and time. 3-APBA@AuNPs showed a stable SPR intensity and forms a reversible tetrahedral ester complex with the analyte L-lactate (100 mM) resulting the NPs aggregation and revealing the blue shift of UV-VIS absorption wavelength (λ = 300 nm to 288 nm). Nestle- Lactogen, an India commercial milk powder has been used for the standardization study of lactate sensing. The milk samples spiked with L-Lactate (1-20mM) showed an increase in UV-VIS absorption peak intensity with concentration, and estimated the lower detection limit (LOD) = 1.1 mM using the calibration graphs. The optical sensing mechanism is explained may be due to π-π* transition of AuNPs stabilized by tetragonal complex of L-lactate bonded to 3-boronate via nucleophilic attack on boron atom. The nanosensor data was validated with commercial Megazyme kit and conventional HPLC technique. In commercial product Amul-India milk, the L-lactate value estimated as 0.678Mm with 95% correlation. Hence, the proposed sensor technique could be an alternate to the high cost conventional methods and at next level, it can be interfaced to smart phone to develop an onsite food, pharma and clinical device applications.