Recent Advances of Plasmon-Enhanced Spectroscopy at Bio-Interfaces. In: Ozaki Y, Schatz GC, Graham D, Itoh T, editors. Frontiers of Plasmon Enhanced Spectroscopy Volume 2. Washington: American Chemical Society; 2016. pp. 183-207. [DOI: 10.1021/bk-2016-1246.ch008]

SERS tags derived from silver nanoparticles and aryl diazonium salts for cell Raman imaging

The surface functionalization of silver nanoparticles (NPs) by Raman reporters has stimulated a wide interest in recent years for the design of Surface-Enhanced Raman Spectroscopy (SERS) labels. However, silver NPs are prone to oxidation and aggregation, which strongly limits their applications. The design of stable SERS tags based on Ag NPs still represents a major challenge for Raman bioimaging. We address this issue herein by taking advantage of aryl diazonium salt chemistry to obtain stable Ag NPs functionalized by multifunctional polyaryl layers bearing different Raman reporters (-NO₂, -CN, -CCH). The resulting SERS-encoded Ag NPs were characterized by UV-vis absorption, transmission electron microscopy (TEM) and SERS. The formation of multilayers at the surface of Ag NPs gives access to new spectrally distinguishable SERS codes thus broadening the library of available Raman tags. Proof-of-concept Raman imaging experiments were performed on cancer cells (HeLa) after NP uptake, highlighting the large potentials of diazonium salt chemistry to design Ag NPs-based SERS labels for Raman bioimaging.

Infrared Metasurface Augmented by Deep Learning for Monitoring Dynamics between All Major Classes of Biomolecules

Insights into the fascinating molecular world of biological processes are crucial for understanding diseases, developing diagnostics, and effective therapeutics. These processes are complex as they involve interactions between four major classes of biomolecules, i.e., proteins, nucleic acids, carbohydrates, and lipids, which makes it important to be able to discriminate between all these different biomolecular species. In this work, a deep learning-augmented, chemically-specific nanoplasmonic technique that enables such a feat in a label-free manner to not disrupt native processes is presented. The method uses a highly sensitive multiresonant plasmonic metasurface in a microfluidic device, which enhances infrared absorption across a broadband mid-IR spectrum and in water, despite its strongly overlapping absorption bands. The real-time format of the optofluidic method enables the collection of a vast amount of spectrotemporal data, which allows the construction of a deep neural network to discriminate accurately between all major classes of biomolecules. The capabilities of the new method are demonstrated by monitoring of a multistep bioassay containing sucrose- and nucleotides-loaded liposomes interacting with a small, lipid membrane-perforating peptide. It is envisioned that the presented technology will impact the fields of biology, bioanalytics, and pharmacology from fundamental research and disease diagnostics to drug development.

Plasmon-Induced Electrocatalysis with Multi-Component Nanostructures

Noble metal nanostructures are exceptional light absorbing systems, in which electron–hole pairs can be formed and used as “hot” charge carriers for catalytic applications. The main goal of the emerging field of plasmon-induced catalysis is to design a novel way of finely tuning the activity and selectivity of heterogeneous catalysts. The designed strategies for the preparation of plasmonic nanomaterials for catalytic systems are highly crucial to achieve improvement in the performance of targeted catalytic reactions and processes. While there is a growing number of composite materials for photochemical processes-mediated by hot charge carriers, the reports on plasmon-enhanced electrochemical catalysis and their investigated reactions are still scarce. This review provides a brief overview of the current understanding of the charge flow within plasmon-enhanced electrochemically active nanostructures and their synthetic methods. It is intended to shed light on the recent progress achieved in the synthesis of multi-component nanostructures, in particular for the plasmon-mediated electrocatalysis of major fuel-forming and fuel cell reactions.

Quantifying the Limits of Detection of Surface-Enhanced Infrared Spectroscopy with Grating Order-Coupled Nanogap Antennas

Infrared spectroscopy is widely used for biomolecular studies, but struggles when investigating minute quantities of analytes due to the mismatch between vibrational cross sections and IR wavelengths. It is therefore beneficial to enhance absorption signals by confining the infrared light to deeply subwavelength volumes comparable in size to the biomolecules of interest. This can be achieved with surface-enhanced infrared absorption spectroscopy, for which plasmonic nanorod antennas represent the predominant implementation. However, unifying design guidelines for such systems are still lacking. Here, we introduce an experimentally verified framework for designing antenna-based molecular IR spectroscopy sensors. Specifically, we find that in order to maximize the sensing performance, it is essential to combine the signal enhancement originating from nanoscale gaps between the antenna elements with the enhancement obtained from coupling to the grating order modes of the unit cell. Using an optimized grating order-coupled nanogap design, our experiments and numerical simulations show a hotspot limit of detection of two proteins per nanogap. Furthermore, we introduce and analyze additional limit of detection parameters, specifically for deposited surface mass, in-solution concentration, and secondary structure determination. These limits of detection provide valuable reference points for performance metrics of surface-enhanced infrared absorption spectroscopy in practical applications, such as the characterization of biological samples in aqueous solution.