Collection Method of SERS Active Nanoparticles for Sensitive and Precise Measurements.

Developing surface-enhanced Raman spectroscopy (SERS) based biosensors requires not only synthesizing SERS active nanoparticles or nanoprobes that produce intense signal but also collecting them in a consistent manner to obtain sensitive and precise measurements. Nanoprobes are commonly measured in solution; however, this approach has several disadvantages that can reduce sensitivity, such as probing only a small percentage of the nanoprobes present in the sample. In this work, a novel collection device was designed, built, and tested which consistently concentrates nanoprobes in a specific area to yield highly sensitive (femtomolar) and repeatable measurements. A particular silica nanoprobe composed of aggregated silver nanoparticles with Raman reporters on them was synthesized and functionalized to measure it on the collection device. The collection device was assessed by collecting several concentrations of nanoprobes and comparing their SERS intensities to determine their limit of detection and the precision on the device. In addition, a competitive binding assay to detect cardiac Troponin I (cTnI) was used as an example to demonstrate the functionality of the nanoprobe and collection device. Nanoprobe samples (10 μL) were detected with less than 10% coefficient of variation (CV) across a range from nearly 27.4 fM to 1.7 pM using the described collection method. In the example assay, several cTnI concentrations ranging from 0 to 250 ng/mL were detected.