Tailoring carbon for single molecule detection – Broad spectrum 3D quantum sensor

Abstract

Current single-molecule SERS sensing is mostly done by plasmonic materials like Gold and Silver due to higher enhancement efficiency. However, plasmonic materials suffer from inherent disadvantages, including inconsistent spectral signature and non-biocompatibility. Researchers are actively searching for a replacement with superior biocompatibility and a uniform spectral signature. Quantum scale Graphene-based SERS signifies a newfound frontier in this regard, owing to high surface area and tunable optical and electronic properties. The use of GQD as a SERS sensor is still critically impeded by low enhancement factor as well as inferior sensitivity due to wavelength-dependent fluorescence property. In this work, we introduce a 3-D Graphene Oxide Quantum sensor (GOQS) with an unmatched enhancement of 1014, enabling ultra-sensitive detection with a limit of detection down to single molecule sensitivity. With 3-D architecture, the interference of the inherent fluorescence of GQD is eliminated, thereby achieving a relatively high enhancement factor on par with plasmonic materials. The high enhancement factor is a combined effect of quantum confinement, edge effects, and charge transfer through molecular adsorption. The single molecule sensitivity (10 −15 M) was experimentally verified using a Raman Probe molecule (CV, R6 G) with excellent repeatability. As a distinct confirmation of single molecule sensitivity of GOQS, we have detected two Raman probe molecules (CV, R6 G) simultaneously, thereby systematically computing the probability of detecting at 10 -15 M level. The ability to detect and distinguish Raman probe molecules simultaneously down to femtomolar level is the lowest limit of detection reported in a non-plasmonic sensor thus far. GOQS was demonstrated for the detecting of disease biomarkers and using Tryptophan. An environmental contaminant Bisphenol-A was detected at a concentration of 10−15 M, corresponding to 2000 ppb. The experimental results indicate a new paradigm towards the activation of quantum scale graphene as a broad-spectrum SERS sensor for numerous ultra-trace analysis.