Phosphoric Acid Induced Controllable Nanoparticle Aggregation for Ultrasensitive SERS Detection of Malondialdehyde in a Microfluidic Chip

Malondialdehyde (MDA), one of the most important products of lipid peroxidation, has been widely accepted as a biomarker to indicate food rancidity as well as the progress of some human diseases. However, ready detection of MDA with ultra-high sensitivity remains a challenge. In this work, a microfluidic surface-enhanced Raman scattering (SERS) sensing chip based on phosphoric acid induced nanoparticles aggregation was proposed for ultrasensitive MDA detection. The sensing chip was composed of an ultrafast microfluidic mixer, which efficiently transferred analytes to hot spots via the mixer assisted hot spots occupying (MAHSO) SERS strategy. Phosphoric acid, a reagent used in MDA detection, played the role of aggregator to induce aggregation of silver nanoparticles (Ag NPs); meanwhile, as fast as a few milliseconds mixing time effectively prevented over-aggregation of Ag NPs. Therefore, this process generated a uniform and dense SERS substrate with analyte molecules located in hot spots. As a result, the MDA SERS sensing chip possessed a limit of detection (LOD) lower than 3.3 x 10(-11) M, high spot-to-spot uniformity with a relative standard deviation (RSD) of 9.0% and an excellent batch-to-batch reproducibility with a RSD of 3.9%. This method also demonstrated excellent specificity and reliability in real sample detection with recoveries of 90.4-109.8% in spiked tests.