Low-cost and high sensitivity glucose sandwich detection using a plasmonic nanodisk metasurface

Metasurface-enhanced biomedical spectroscopy

Enhancing the sensitivity of biomedical spectroscopy is crucial for advancing medical research and diagnostics. Metasurfaces have emerged as powerful platforms for enhancing the sensitivity of various biomedical spectral detection technologies. This capability arises from their unparalleled ability to improve interactions between light and matter through the localization and enhancement of light fields. In this article, we review representative approaches and recent advances in metasurface-enhanced biomedical spectroscopy. We provide a comprehensive discussion of various biomedical spectral detection technologies enhanced by metasurfaces, including infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and other spectral modalities. We demonstrate the advantages of metasurfaces in improving detection sensitivity, reducing detection limits, and achieving rapid biomolecule detection while discussing the challenges associated with the design, preparation, and stability of metasurfaces in biomedical detection procedures. Finally, we explore future development trends of metasurfaces for enhancing biological detection sensitivity and emphasize their wide-ranging applications.

Au Nanorings/TiO2 NPs@MXene-Based Metasurfaces with a Magnetic Mirror-Modulated ECL Strategy for Extracellular Vesicle Detection

A metasurface as an artificial electromagnetic structure can concentrate optical energy into nanometric volumes to strongly enhance the light-matter interaction, which has been becoming a powerful platform for optical sensing, nonlinear effects, and quantum optics. Herein, we developed a novel hybrid plasmonic-dielectric metasurface consisting of Au nanorings (Au NRs) and TiO2 nanoparticles derived from MXene (TiO2 NPs@MXene). The hybrid metasurface simultaneously benefited from the high near-field enhancement effect of plasmonic materials and the low loss of dielectric materials. Furthermore, the optical modulation efficiency of the hybrid metasurface can be regulated by a magnetic mirror configuration. The magnetic mirror acted like a mirror, confining the electrons to a limited region and increasing the density of the surface plasmon. Moreover, the electrochemiluminescence (ECL) of the Cu2BDC metal-organic framework (Cu2BDC-MOF) served as a light source for the Au NRs/TiO2 NPs@MXene metasurface. Due to the exceptional light manipulation capability of the hybrid metasurface and the coordination of the magnetic mirror, the isotropic ECL signal can be dynamically amplified and converted into polarized emission. Finally, a metasurface-regulated ECL (MECL)-based biosensor with a dual-positive membrane protein recognition strategy was developed for the accurate identification of gastric cancer-derived extracellular vesicles. The novel MECL research opened up a new route in the realization of dynamically tunable metasurfaces for optical sensing and novel nanophotonic devices.

Dynamically Metasurface-Modulated Electrochemiluminescence Polarization Coupling Angle Strategy for miR-142-3p Detection

The combination of the electrochemiluminescence (ECL) technique with nanophotonics research can spark new analytical and sensing applications. Herein, we developed a novel modulation strategy of the ECL polarization angle based on the dynamically tunable few-layer metasurface. The bilayer metasurface consisted of a fixed Au-Ag core-shell nanocube array (Au@Ag NCA) layer with strong plasmonic hot spots and different amounts of the Au nanoparticles@MoS2 heterostructure nanosheet (0D-2D HNS) layer with strong metal-support interaction. Due to the interference and near-field coupling between layers, the bilayer metasurface can strongly redistribute the local electromagnetic field and energy in the ECL system, which not only significantly amplified the ECL signal but also modulated the polarization coupling angle. Therefore, the novel ECL polarization angle-resolved sensing strategy has been developed, which was beneficial to improve the sensitivity and resolution of ECL sensing. A dynamically tunable metasurface-based ECL biosensor was successfully used to detect the asthma-related miRNA-142-3p (miR-142-3p). Moreover, the simulation calculations of the electromagnetic field revealed the unique optical activity of the metasurface. This study brought the insightful understanding of the metasurface-modulated optical signal and provided a new idea to construct novel sensing platforms.

An Active Electromagnetically Induced Transparency (EIT) Metamaterial Based on Conductive Coupling

In this paper, we demonstrate an active metamaterial manifesting electromagnetically induced transparency (EIT) effect in the microwave regime. The metamaterial unit cell consists of a double-cross structure, between which a varactor diode is integrated. The capacitance of the diode is controlled by a reversed electrical bias voltage supplied through two connected strip lines. The diode behaves as a radiative resonant mode and the strip lines as a non-radiative resonant mode. The two modes destructively interference with each other through conductive coupling, which leads to a transmission peak in EIT effect. Through electrical control of the diode capacitance, the transmission peak frequency is shifted from 7.4 GHz to 8.7 GHz, and the peak-to-dip ratio is tuned from 1.02 to 1.66, demonstrating a significant tunability.

Surface Functionalization and Texturing of Optical Metasurfaces for Sensing Applications

Optical metasurfaces are planar metamaterials that can mediate highly precise light-matter interactions. Because of their unique optical properties, both plasmonic and dielectric metasurfaces have found common use in sensing applications, enabling label-free, nondestructive, and miniaturized sensors with ultralow limits of detection. However, because bare metasurfaces inherently lack target specificity, their applications have driven the development of surface modification techniques that provide selectivity. Both chemical functionalization and physical texturing methodologies can modify and enhance metasurface properties by selectively capturing analytes at the surface and altering the transduction of light-matter interactions into optical signals. This review summarizes recent advances in material-specific surface functionalization and texturing as applied to representative optical metasurfaces. We also present an overview of the underlying chemistry driving functionalization and texturing processes, including detailed directions for their broad implementation. Overall, this review provides a concise and centralized guide for the modification of metasurfaces with a focus toward sensing applications.

Ultrasensitive Molecular Detection at Subpicomolar Concentrations by the Diffraction Pattern Imaging with Plasmonic Metasurfaces and Convex Holographic Gratings

Compact and cost-effective optical devices for highly sensitive detection of trace molecules are significant in many applications, including healthcare, pollutant monitoring and explosive detection. Nanophotonic metasurface-based sensors have been intensively attracting attentions for molecular detection. However, conventional methods often involve spectroscopic characterizations that require bulky, expensive and sophisticated spectrometers. Here, a novel ultrasensitive sensor of plasmonic metasurfaces is designed and fabricated for the detection of trace molecules. The sensor features a convex holographic grating, of which the first-order diffraction pattern of a disposable metasurface is recorded by a monochrome camera.The diffraction pattern changes with the molecules attached to the metasurface, realizing label-free and spectrometer-free molecular detection by imaging and analyzing of the diffraction pattern. By integrating the sensor with a microfluidic setup, the quantitative characterization of rabbit anti-human Immunoglobulin G (IgG) and human IgG biomolecular interactions is demonstrated with an excellent limit of detection (LOD) of 0.6 pm. Moreover, both the metasurface and holographic grating are obtained through vacuum-free solution-processed fabrications, minimizing the manufacturing cost of the sensor. A prototype of the imaging-based sensor, consisting of a white light-emitting diode (LED) and a consumer-level imaging sensor is achieved to demonstrate the potential for on-site detection.

Research of Gate-Tunable Phase Modulation Metasurfaces Based on Epsilon-Near-Zero Property of Indium-Tin-Oxide

In this paper, we proposed a reflection phase electrically tunable metasurface composed of an Au/Al2O3/ITO/Au grating structure. This antenna array can achieve a broad phase shift continuously and smoothly from 0° to 320° with a 5.85 V applied voltage bias. Tunability arises from field-effect modulation of the carrier concentrations or accumulation layer at the Al2O3/ITO interface, which excites electric and magnetic resonances in the epsilon-near-zero region. To make the reflected phase tuning range as wide as possible, some of the intensity of the reflected light is lost due to the excited surface plasmon effect. Simulation results show that the effect of optimal phase modulation can be realized at a wavelength range of 1550 nm by modulating the carrier concentration in our work. Additionally, we utilized an identical 13-unit array metasurface to demonstrate its application to the beam steering function. This active optical metasurface can enable a new realm of applications in ultrathin integrated photonic circuits.

Glucose detection through surface-enhanced Raman spectroscopy: A review

Glucose detection is of vital importance to diabetes diagnosis and treatment. Optical approaches in glucose sensing have received much attention in recent years due to the relatively low cost, portable, and mini-invasive or non-invasive potentials. Surface enhanced Raman spectroscopy (SERS) endows the benefits of extremely high sensitivity because of enhanced signals and specificity due to the fingerprint of molecules of interest. However, the direct detection of glucose through SERS was challenging because of poor adsorption of glucose on bare metals and low cross section of glucose. In order to address these challenges, several approaches were proposed and utilized for glucose detection through SERS. This review article mainly focuses on the development of surface enhanced Raman scattering based glucose sensors in recent 10 years. The sensing mechanisms, rational design and sensing properties to glucose are reviewed. Two strategies are summarized as intrinsic sensing and extrinsic sensing. Four general categories for glucose sensing through SERS are discussed including SERS active platform, partition layer functionalized surface, boronic acid based sensors, and enzymatic reaction based biosensors. Finally, the challenges and outlook for SERS based glucose sensors are also presented.

Quantification of Glucose, fructose and 1,5-Anhydroglucitol in plasma of diabetic patients by ultra performance liquid chromatography tandem mass spectrometry

Type 2 diabetes mellitus (T2DM), a worldwide disease that affects the quality of human life and social development. Glucose, fructose and 1,5-anhydroglucitol are closely related to diabetes mellitus. However, few methods have been reported to achieve these three carbohydrates in the blood simultaneously. In this study, a UPLC-MS/MS method allowing to quantify glucose, fructose, and 1,5-anhydroglucitol simultaneously in human plasma was developed. The analysis was performed by UPLC-MS/MS system with HILIC column. This new method provided satisfactory results in terms of calibration curves with good linearity (R² > 0.99) over 3 order of magnitude range, precision (coefficient of variation of intra-day and inter-day: 0.72-10.23% and 2.21-13.8%), accuracy (results of intra-day and inter-day: 97-113%, 100-107%), matrix effects (87-109%), recovery (93-119%), carry-over (0.004-0.014%), as well as stability (0.04-6.9%) within the acceptance criteria. The reproducible, precise and accurate method with suitable dynamic ranges was successfully applied to the analysis of glucose, fructose and 1,5-anhydroglucitol in T2DM under different pathophysiological conditions.

Emerging Theranostic Nanomaterials in Diabetes and Its Complications

Diabetes mellitus (DM) refers to a group of metabolic disorders that are characterized by hyperglycemia. Oral subcutaneously administered antidiabetic drugs such as insulin, glipalamide, and metformin can temporarily balance blood sugar levels, however, long-term administration of these therapies is associated with undesirable side effects on the kidney and liver. In addition, due to overproduction of reactive oxygen species and hyperglycemia-induced macrovascular system damage, diabetics have an increased risk of complications. Fortunately, recent advances in nanomaterials have provided new opportunities for diabetes therapy and diagnosis. This review provides a panoramic overview of the current nanomaterials for the detection of diabetic biomarkers and diabetes treatment. Apart from diabetic sensing mechanisms and antidiabetic activities, the applications of these bioengineered nanoparticles for preventing several diabetic complications are elucidated. This review provides an overall perspective in this field, including current challenges and future trends, which may be helpful in informing the development of novel nanomaterials with new functions and properties for diabetes diagnosis and therapy.

Trending Technology of Glucose Monitoring during COVID-19 Pandemic: Challenges in Personalized Healthcare

The COVID-19 pandemic has continued to spread rapidly, and patients with diabetes are at risk of experiencing rapid progression and poor prognosis for appropriate treatment. Continuous glucose monitoring (CGM), which includes accurately tracking fluctuations in glucose levels without raising the risk of coronavirus exposure, becomes an important strategy for the self-management of diabetes during this pandemic, efficiently contributing to the diabetes care and the fight against COVID-19. Despite being less accurate than direct blood glucose monitoring, wearable noninvasive systems can encourage patient adherence by guaranteeing reliable results through high correlation between blood glucose levels and glucose concentrations in various other biofluids. This review highlights the trending technologies of glucose sensors during the ongoing COVID-19 pandemic (2019-2020) that have been developed to make a significant contribution to effective management of diabetes and prevention of coronavirus spread, from off-body systems to wearable on-body CGM devices, including nanostructure and sensor performance in various biofluids. The advantages and disadvantages of various human biofluids for use in glucose sensors are also discussed. Furthermore, the challenges faced by wearable CGM sensors with respect to personalized healthcare during and after the pandemic are deliberated to emphasize the potential future directions of CGM devices for diabetes management.

Metal-Modified Montmorillonite as Plasmonic Microstructure for Direct Protein Detection

Thanks to its negative surface charge and high swelling behavior, montmorillonite (MMT) has been widely used to design hybrid materials for applications in metal ion adsorption, drug delivery, or antibacterial substrates. The changes in photophysical and photochemical properties observed when fluorophores interact with MMT make these hybrid materials attractive for designing novel optical sensors. Sensor technology is making huge strides forward, achieving high sensitivity and selectivity, but the fabrication of the sensing platform is often time-consuming and requires expensive chemicals and facilities. Here, we synthesized metal-modified MMT particles suitable for the bio-sensing of self-fluorescent biomolecules. The fluorescent enhancement achieved by combining clay minerals and plasmonic effect was exploited to improve the sensitivity of the fluorescence-based detection mechanism. As proof of concept, we showed that the signal of fluorescein isothiocyanate can be harvested by a factor of 60 using silver-modified MMT, while bovine serum albumin was successfully detected at 1.9 µg/mL. Furthermore, we demonstrated the versatility of the proposed hybrid materials by exploiting their plasmonic properties to develop liquid label-free detection systems. Our results on the signal enhancement achieved using metal-modified MMT will allow the development of highly sensitive, easily fabricated, and cost-efficient fluorescent- and plasmonic-based detection methods for biomolecules.

Construction of a selective non-enzymatic electrochemical sensor based on hollow nickel nanospheres/carbon dots–chitosan and molecularly imprinted polymer film for the detection of glucose

A non-enzymatic glucose electrochemical sensor platform was fabricated by assembling hollow nickel nanospheres/carbon dots–chitosan and molecularly imprinted polymer film modified a glass carbon electrode.

Probing blood plasma samples for the detection of diabetes using SERS aided by PCA and LDA multivariate data analyses

Fabrication of a SERS-active substrate using Langmuir–Blodgett and self-assembly techniques for the detection of diabetes from blood plasma samples.

Plasmon-driven protodeboronation reactions in nanogaps

Boronic acids are the key compounds in Suzuki coupling reactions and in the detection of monosaccharides. The C-B bond cleavage deboronation is an important side reaction that lowers the Suzuki coupling reaction yield and even disables saccharide detection. Here, we report that protodeboronation occurs for 4-mercaptophenylboronic acid (MPBA) within narrow nanogaps between gold nanoparticles (AuNPs) and planar gold substrates. The irradiation of such nanoparticle-on-mirror (NPoM) systems at 785 nm drives the protodeboronation reaction to form benzenethiol (BT). Wavelength-dependence experiments, combined with dark-field single-particle scattering spectroscopy, reveal that excitation of the bonding dipole plasmon mode of the NPoM leads to the best efficiency. Among the excited plasmon decay pathways, the generation of hot charge carriers induces the protodeboronation of MPBA. The possibility of plasmonic thermal reactions is ruled out because external heating of the substrates does not cause the reaction to take place. A comparison of the reaction yield under ambient, Ar, and oxygen gas conditions reveals that hot charge carriers directly transfer to MPBA, which subsequently produces BT, but the presence of oxygen promotes the reaction by opening another hot-electron transfer channel. The protodeboronation reaction of MPBA is an important addition to the catalog of plasmon-driven chemical reactions, not only because the reaction is relevant to organic and analytical chemistry but also because it deepens our understanding of the hot carrier dynamics at the interface between plasmonic nanoparticles and molecules.