Identification and quantification of illicit drugs using nanodendritic surface-enhanced Raman scattering substrates

Surface-enhanced Raman scattering (SERS) is an analytical detection method with the potential to provide ultrasensitive detection of analytes in a variety of applications, including forensic science, environmental monitoring and medical diagnostics. In this work, we demonstrate rapid, sensitive and specific detection of illicit drugs in both aqueous samples and saliva using SERS substrates with a unique, dendritic architecture. The substrates are prepared on a reusable microelectrode platform through the controlled assembly of colloidal silver nanoparticles from a droplet. Identification and quantification of illicit drugs is accomplished on these substrates with the aid of Principal Component Analysis (PCA) coupled with a Support Vector Machine (SVM). We demonstrate 100% accuracy in the detection of four different illicit drugs (cocaine, heroin, THC, and oxycodone), and 98.3% accuracy in the quantification of cocaine across four orders of magnitude. Finally, we demonstrate a simple method, with limited sample processing, for the ultrasensitive detection of cocaine in saliva to a limit of detection of 100 ppb.

SERS substrates are typically produced through methods that require micro/nanofabrication, which poses a barrier to their popularization. Here we will also briefly report on a facile and rapid approach to prepare ultrasensitive SERS substrates in low-resource settings. We demonstrate the unique characteristic of this method to produce highly SERS-active surfaces from a wide range of materials, including commercially available glass slides pre-coated with indium tin oxide (ITO). Finally, we show that these substrates can detect trace quantities of explosives, drugs and pesticides, with sensitivities superior to some commercially available products.