A graphene‐Au nano‐pyramid hybrid system that enables label‐free single molecule detection is demonstrated. The bio‐compatible graphene‐based SERS platform boosts a high density of hot spots with local SERS enhancement factor over 1010. We demonstrate that graphene can play a key role in quantitative study of SERS mechanisms, and can also serve as a promising building block in SERS active structures especially for biosensor applications.

The unique properties of graphene when coupled to plasmonic surfaces render a very interesting physical system with intriguing responses to stimuli such as photons. It promises exciting application potentials such as photodetectors as well as biosensing. With its semimetallic band structure, graphene in the vicinity of metallic nanostructures is expected to lead to non-negligible perturbation of the local distribution of electromagnetic field intensity, an interesting plasmonic resonance process that has not been studied to a sufficient extent. Efforts to enhance optoelectronic responses of graphene using plasmonic structures have been demonstrated with rather modest Raman enhancement factors of less than 100. Here, we examine a novel cooperative graphene-Au nanopyramid system with a remarkable graphene Raman enhancement factor of up to 10(7). Experimental evidence including polarization-dependent Raman spectroscopy and scanning electron microscopy points to a new origin of a drastically enhanced D-band from sharp folds of graphene near the extremities of the nanostructure that is free of broken carbon bonds. These observations indicate a new approach for obtaining detailed structural and vibrational information on graphene from an extremely localized region. The new physical origin of the D-band offers a realistic possibility of defining active devices in the form of, for example, graphene nanoribbons by engineered graphene folds (also known as wrinkles) to realize edge-disorder-free transport. Furthermore, the addition of graphene made it possible to tailor the biochemical properties of plasmonic surfaces from conventional metallic ones to biocompatible carbon surfaces.

Ultrasensitive detection and spatially resolved mapping of neurotransmitters, dopamine and serotonin, are critical to facilitate understanding brain functions and investigate the information processing in neural networks. In this work, we demonstrated single molecule detection of dopamine and serotonin using a graphene–Au nanopyramid heterostructure platform. The quasi-periodic Au structure boosts high-density and high-homogeneity hotspots resulting in ultrahigh sensitivity with a surface enhanced Raman spectroscopic (SERS) enhancement factor ∼1010. A single layer graphene superimposed on a Au structure not only can locate SERS hot spots but also modify the surface chemistry to realize selective enhancement Raman yield. Dopamine and serotonin could be detected and distinguished from each other at 10–10 M level in 1 s data acquisition time without any pretreatment and labeling process. Moreover, the heterostructure realized nanomolar detection of neurotransmitters in the presence of simulated body fluids. These findings represent a step forward in enabling in-depth studies of neurological processes including those closely related to brain activity mapping (BAM).