Surface-enhanced Raman spectroscopy (SERS) has made significant progress in recent decades, primarily driven by the principles of plasmon on metal surfaces. In contrast, SERS on non-metal substrates is based on the chemical mechanism involving charge transfer (CT) processes within irradiated molecules and the resonance Raman effect. This plasmon-free SERS mechanism proves highly suitable for detecting biomedical samples, as it suppresses the photo-thermal conversion associated with plasmon. In this study, we developed non-metal SERS substrates using conducting polymer nanofibers through electropolymerization. We evaluated the CT process and performance of the conducting polymer SERS substrates.

We will discuss here a new seed-mediated synthesis of BGNS-Ag in which the morphology of the BGNS-Ag can be tuned precisely. Thus their plasmon resonances can be tuned by changing the concentration of the chemicals required in this synthesis. Herein we show how the concentration of AgNO3 plays a significant role in the spike length and spike sharpness. To illustrate the usefulness of the BGNS-Ag morphology in practical real-world in-field applications, we will discuss that the BGNS-Ag can be utilized as a solution-based SERS detection of a variety of analytes including illegal drugs (heroin, cocaine, and fentanyl), biomarkers (pyocyanin, methimazole), pesticides (thiram, ziram), and many more.

We develop highly sensitive graphene-based surface-enhanced Raman spectroscopy (SERS) substrates where monolayer graphene is coated on the Ag/mica substrates. SERS has attracted attention in biosensor applications that allow label-free detection with high specificity. Recently two-dimensional (2D) materials such as graphene, h-BN, and MoS2 have been explored as a new platform for SERS substrates. These materials have the advantage of being non-metal, with excellent biological compatibility, endurance, and uniformity characteristics. Then, we study the stacked SERS substrates where monolayer graphene is transferred on the mica substrates with single-crystal Ag thin films deposited on the back to improve SERS efficiency. The fabricated SERS substrates show stronger Raman signals than the mica substrates with Ag thin films. Then sandwich enzyme-linked immunosorbent assay (ELISA) is fabricated on the SERS substrates to detect bovine interleukin-6 (IL-6), inciting bovine mastitis.

To improve the LFIA sensitivity, we have utilized high aspect-ratio plasmonic gold nanostars (GNS), which possess higher optical brightness than traditional gold nanospheres. We will discuss here the surfactant-free GNS synthesis in which the aspect ratio of the GNS can be tuned by changing the concentration of three reagents, ascorbic acid, silver nitrate (AgNO3), and hydrochloric acid (HCl). Herein, we selected the bacterium Yersinia pestis as a model analyte system, and the LFIA efficiency was investigated with the optical density measurements of the test line by utilizing different aspect-ratio GNSs. Our results showed that the maximum LFIA sensitivity was achieved with the GNS morphology having the maximum aspect-ratio spikes. Compared to other nanoparticle-based LFIA systems, high aspect-ratio GNS exhibits high analytical sensitivity, indicating it to be a promising candidate to become a much more versatile and tunable LFIA sensor.

Unlocking the potential of colloidal metamaterials—artificial materials mirroring molecular structures—holds promise for diverse applications, from optical engineering to catalytic chemistry. Yet, orchestrating precise self-assembly of colloidal metamaterials remains challenging due to the lack of regioselective surface chemistry. Addressing this, we introduce a novel strategy employing DNA-patched nanoparticles to drive the self-assembly of colloidal metamolecules. By utilizing magnetic bead-assisted DNA cluster transfer, we overcome geometrical constraints, enabling regioselective DNA patches. This approach is highly scalable and versatile, affording diverse configurations. We showcase the creation of gold and silver nanoparticle-based colloidal metamolecules, demonstrating the strategy's broad applicability. Notably, we employ this method to position fluorescent nanodiamonds within silver nanocube dimers, enabling precise control over photophysical properties. Our approach revolutionizes colloidal metamaterial synthesis, paving the way for tailored nanoscale functionalities in fields such as biological sensing and optical physics.

We propose and experimentally demonstrate a surface plasmon resonance sensor based on D-shaped single mode silica optical fiber and Indium Tin Oxide (ITO) that operate in the infrared wavelength region. The experimental result revealed that, a sensor fabricated with 0.6dB insertion loss and coated with 120nm thickness ITO layer presented a resonance in the wavelength range of 1200nm - 1400nm, and a refractive index sensitivity of 1409.34 nm/RIU with R-squared 0.99 for the range 1.33 - 1.42 RIU. We investigated also the effects of the polishing depth of D-shaped fiber and the thickness of ITO film on the performance of the sensor sensitivity. Both the experimental result and the COMSOL numerical simulation result indicate that when the thickness of ITO film increases, the resonance wavelength shift to the longer wavelength. However, in order to ensure that the sensor performance is not affected, the polishing depth should be appropriately reduced when the thickness of ITO film is increases; conversely, when the thickness of ITO film decreases, the polishing depth should be increased.

We fabricated and characterized sensitivity enhanced surface plasmon resonance sensor based on cladding etched multimode polymer optical fiber coated with gold/Indium Tin Oxide (ITO) bilayer. The fibre use for experiment has a core and cladding of 486μm and 500 μm, respectively. The cladding is completely etched out from 1cm long section of a piece of fibre using Dimethyl Sulfoxide. The etched section of the fiber is coated with 40nm gold layer followed by 30nm ITO layer. The sensor was tested by immersing it in a glucose solution of different refractive index ranging from 1.33 to 1.40. The experimental result shows that, the sensor exhibited a refractive index sensitivity of 2053 nm/RIU for the range 1.33-1.37 RIU and 3081 nm/RIU for the range 1.37-1.40 RIU, both with R-squared of 0.99. These sensitivity values are higher than other sensitivity enhancement approaches reported in the literatures. We belive that, the proposed sensor has the advantages of simple structure and easy fabrication process (which does not require tedious side polishing), cost effective and high sensitivity, which has a potential prospect in the field of biosensing and chemical sensing.

We present a Surface Plasmon Resonance Imaging (SPRI) biochip system to quantitatively detect micro-RNAs involved in the cytokine storm during an inflammatory response. The thiol composition of the self-assembled monolayer on the biochip gold surface was tuned to maximize the capture of RNAs at low concentrations. To further amplify this signal, we have developed a sandwich-like assay using oligonucleotides functionalized gold nanoparticles (AuNPs), synthesized at ambient temperature and optimized to have a high solubility in saline solutions. Sub-picomolar detection limit of those small RNAs was achieved with all these combined improvements.