The Haynes group has a long history of research in SERS, especially in the application of SERS for biosensing, and focuses on two areas: substrate design and signal transduction mechanisms. Our group works on multiple types of substrates, such as metal film-over-nanospheres (MFONs) and nanoparticle colloids, to develop inexpensive and simple substrates with high SERS enhancement factors without requiring advanced lithographic techniques. Current work in the group focuses on synthesizing chiral gold nanoparticles as well as silica-coated gold nanorods to detect specific analytes with high sensitivity. We also investigate different methods to facilitate signal transduction, such as using affinity agents with physical or chemical affinity for the analyte to bring analytes closer to the high enhancement region of SERS substrates or using the structure of a substrate to physically trap analytes within the enhancement region. Current work in this area includes the use of linear polymers as affinity agents for a wide range of analytes such as different strains of bacteria and using nanogaps in MFON substrates to trap and detect virus-like particles. Additionally, our group employs machine learning techniques such as principal component analysis (PCA) and support vector machines (SVM) to aid in data analysis and classification of samples from their Raman spectra.

Silica nanoparticles have been previously used in the Haynes group for a range of biomedical applications. In recent years, our work has shifted towards leveraging our knowledge from biomedicine towards designing, synthesizing, and characterizing silica-based nanoparticles for agriculture and other applications. We use our chemical expertise to tune various nanoparticle characteristics such as size, porosity, dissolution rate, surface charge, and functionalization with the overall goal of measuring their impact on different plant models. Our projects have focused on tuning the dissolution of silica nanoparticles for applications in watermelon as well as coating porous silica nanoparticles with chitosan for applications in watermelon and soybeans. We are also interested in using responsive nanoparticles as delivery agents for various cargo. The Haynes group employs various nanoparticle synthesis methods as well as numerous characterization techniques such as dynamic light scattering, nitrogen physisorption, transmission electron microscopy, energy dispersive spectroscopy, confocal microscopy, and X-ray photoelectron spectroscopy, among others. Many of our projects in this area are collaborations with scientists at a range of academic, government, and commercial institutions. Overall, our work is contributing towards nano-enabled agricultural applications that can increase crop production and reduce plant disease progression to strive towards meeting UN Sustainable Development Goals.

The Haynes Lab has been active in analytical electrochemistry since its very start, specifically micro-electrochemistry. Rather than large electrodes, we use in carbon-fiber microelectrodes. Made using glass capillary tubes and carbon-fiber, these microelectrodes allow electrochemical detection at the single-cell level. This means that they provide higher spatial and temporal resolution compared to typical electrode systems, with the ability to measure extracellular and intercellular analytes of interest. Past studies have focused on understanding cell platelet opioid receptors, tracking serotonin levels in sickle cell disease, and understanding changes in mast cell function in mice with and without malaria. Current studies focus on adapting carbon-fiber microelectrodes with different nanomaterial surface coatings to enhance their sensitivity for analytes of interest, including reactive oxygen species and neurotransmitters. We combine carbon-fiber microelectrodes and carbon dots to produce fluorescent, electrochemical sensors and exploit carbon-fiber microelectrodes to understand nanoparticle transformations. We can perform a wide range of electrochemical techniques from traditional cyclic voltammetry and chronoamperometry to fast scan cyclic voltammetry and single cell amperometry.