Highly sensitive detection of glucose: A quantitative approach employing nanorods assembled plasmonic substrate

Raman silent region - based method for detection of pesticides with cyano group

Based on the fact that not all chemical substances possess good Raman signals, this article focuses on the Raman silent region signals of pesticides with cyano group. Under the optimized conditions of methanol-water (1:1, v/v) as the solvent, irradiation at 302 nm light source for 20 min, and the use of 0.5 mol/L KI as the aggregating agent, Surface-enhanced Raman spectroscopy (SERS) method for azoxystrobin detection was developed by the Raman silent region signal of 2230 cm-1, and verified by detecting the spiked grapes with different concentrations of azoxystrobin. Other four pesticides with cyano group also could be identified at the peak of 2180 cm-1, 2205 cm-1, 2125 cm-1, and 2130 cm-1 for acetamiprid, phoxim, thiacloprid and cymoxanil, respectively. When azoxystrobin or acetamiprid was mixed respectively with chlorpyrifos without cyano group, their SERS signals in the Raman silent region of chlorpyrifos were not interfered, while mixed with cymoxanil in different ratios (1:4, 1:1 and 4:1), respectively, each two pesticides with cyano group could be distinguished by the changes in the Raman silent region. In further, four pesticides with or without cyano group were mixed together in 1:1:1:1 (acetamiprid, cymoxanil, azoxystrobin chlorpyrifos), and each pesticide still could be identified even at 0.5 mg/L. The results showed that the SERS method combined with UV irradiation may provide a new way to monitor the pesticides with C≡N performance in the Raman silent region without interference from the food matrix.

Dual-Probe SERS Nanosensor: A Promising Approach for Sensitive and Ratiometric Detection of Glucose in Clinical Settings

Diabetes is a major global health concern, with millions of annual deaths. Monitoring glucose levels is vital for clinical management, and urine samples offer a noninvasive alternative to blood samples. Optical techniques for urine glucose sensing have gained notable traction due to their cost-effectiveness and portability. Among these methods, surface-enhanced Raman spectroscopy (SERS) has attracted considerable attention thanks to its remarkable sensitivity and multiplexing capabilities. However, challenges remain in achieving reliable quantification through SERS. In this study, an alternative approach is proposed to enhance quantification involving the use of dual probes. Each probe is encoded with unique SERS signatures strategically positioned in the biologically silent region. One probe indicates the glucose presence, while the other acts as an internal reference for calibration. This setup enables ratiometric analysis of the SERS signal, directly correlating it with the glucose concentration. The fabrication of the sensor relies on the prefunctionalization of Fe sheets using an aryl diazonium salt bearing a -C≡CH group (internal reference), followed by the immobilization of Ag nanoparticles modified with an aryl diazonium salt bearing a -B(OH)2 group (for glucose capture). A secondary probe bearing a -B(OH)2 group on one side and a -C≡N group on the other side enables the ratiometric analysis by forming a sandwich-like structure in the presence of glucose (glucose indicator). Validation studies in aqueous solutions and artificial urine demonstrated the high spectral stability and the potential of this dual-probe nanosensor for sensitive glucose monitoring in clinical settings.

Vibrational Spectroscopy in Urine Samples as a Medical Tool: Review and Overview on the Current State-of-the-Art

Although known since the first half of the twentieth century, the evolution of spectroscopic techniques has undergone a strong acceleration after the 2000s, driven by the successful development of new computer technologies suitable for analyzing the large amount of data obtained. Today's applications are no longer limited to analytical chemistry, but are becoming useful instruments in the medical field. Their versatility, rapidity, the volume of information obtained, especially when applied to biological fluids that are easy to collect, such as urine, could provide a novel diagnostic tool with great potential in the early detection of different diseases. This review aims to summarize the existing literature regarding spectroscopy analyses of urine samples, providing insight into potential future applications.

Molecular Level Sucrose Quantification: A Critical Review

Sucrose is a primary metabolite in plants, a source of energy, a source of carbon atoms for growth and development, and a regulator of biochemical processes. Most of the traditional analytical chemistry methods for sucrose quantification in plants require sample treatment (with consequent tissue destruction) and complex facilities, that do not allow real-time sucrose quantification at ultra-low concentrations (nM to pM range) under in vivo conditions, limiting our understanding of sucrose roles in plant physiology across different plant tissues and cellular compartments. Some of the above-mentioned problems may be circumvented with the use of bio-compatible ligands for molecular recognition of sucrose. Nevertheless, problems such as the signal-noise ratio, stability, and selectivity are some of the main challenges limiting the use of molecular recognition methods for the in vivo quantification of sucrose. In this review, we provide a critical analysis of the existing analytical chemistry tools, biosensors, and synthetic ligands, for sucrose quantification and discuss the most promising paths to improve upon its limits of detection. Our goal is to highlight the criteria design need for real-time, in vivo, highly sensitive and selective sucrose sensing capabilities to enable further our understanding of living organisms, the development of new plant breeding strategies for increased crop productivity and sustainability, and ultimately to contribute to the overarching need for food security.

Colorimetric sensing of glucose and GSH using core-shell Cu/Au nanoparticles with peroxidase mimicking activity

The catalytic properties of bimetallic nanoparticles have been widely studied by researchers in many fields. In this paper, core-shell Cu/Au nanoparticles (Cu/Au NPs) were synthesized by a simple and mild one-pot method, and their peroxidase activity was proved by catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with color change to blue. The change of solution color and absorbance strongly depends on the concentration of H₂O₂, so it can be used for direct detection of H₂O₂ and indirect detection of glucose. What's more, GSH can efficiently react with the hydroxyl radicals from H₂O₂ catalyzed by core-shell Cu/Au NPs to inhibit the production of ox-TMB. Thus, the concentration of GSH can be determined by the decrease in the absorbance of the solution at 652 nm. The results showed that our proposed strategy had good detection range and detection limit for the detection of glucose and GSH. This method has been used in the detection of practical samples and has great application potential in environmental monitoring and clinical diagnosis.

Nanomaterials-assisted metabolic analysis toward in vitro diagnostics

In vitro diagnostics (IVD) has played an indispensable role in healthcare system by providing necessary information to indicate disease condition and guide therapeutic decision. Metabolic analysis can be the primary choice to facilitate the IVD since it characterizes the downstream metabolites and offers real-time feedback of the human body. Nanomaterials with well-designed composition and nanostructure have been developed for the construction of high-performance detection platforms toward metabolic analysis. Herein, we summarize the recent progress of nanomaterials-assisted metabolic analysis and the related applications in IVD. We first introduce the important role that nanomaterials play in metabolic analysis when coupled with different detection platforms, including electrochemical sensors, optical spectrometry, and mass spectrometry. We further highlight the nanomaterials-assisted metabolic analysis toward IVD applications, from the perspectives of both the targeted biomarker quantitation and untargeted fingerprint extraction. This review provides fundamental insights into the function of nanomaterials in metabolic analysis, thus facilitating the design of next-generation diagnostic devices in clinical practice.

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.

Recent Advancement in Biofluid-Based Glucose Sensors Using Invasive, Minimally Invasive, and Non-Invasive Technologies: A Review

Biosensors have potentially revolutionized the biomedical field. Their portability, cost-effectiveness, and ease of operation have made the market for these biosensors to grow rapidly. Diabetes mellitus is the condition of having high glucose content in the body, and it has become one of the very common conditions that is leading to deaths worldwide. Although it still has no cure or prevention, if monitored and treated with appropriate medication, the complications can be hindered and mitigated. Glucose content in the body can be detected using various biological fluids, namely blood, sweat, urine, interstitial fluids, tears, breath, and saliva. In the past decade, there has been an influx of potential biosensor technologies for continuous glucose level estimation. This literature review provides a comprehensive update on the recent advances in the field of biofluid-based sensors for glucose level detection in terms of methods, methodology and materials used.

In Situ Microfluidic SERS Chip for Ultrasensitive Hg2+ Sensing Based on I--Functionalized Silver Aggregates

Mercury(II) ions are causing serious environmental pollution and health damage. Developing a simple, rapid, and sensitive sensor for Hg²⁺ detection is of great significance. Herein, we demonstrate an I^--functionalized surface-enhanced Raman scattering (SERS) substrate for rapid and sensitive Hg²⁺ sensing on a highly integrated microfluidic platform. Based on the combination reaction between I^- and Hg²⁺, the Hg²⁺ sensing is achieved via the SERS intensity "turn-off" strategy, where HgI₂ precipitation is formed on an SERS substrate interface, dissociating the Raman reporters that coadsorbed with I^-. Owing to the strong binding constant between I^- and Hg²⁺, our I^--functionalized substrate demonstrates a very fast sensing response (∼150 s). Through reliable in situ SERS detection, a robust calibration curve between the "turn-off" signal and "lgC" is obtained in a broad concentration range of 10^-9 to 10^-13 M. Additionally, the detectable Hg²⁺ concentration can be as low as 1 fM. The good selectivity toward Hg²⁺ is also verified by testing about a dozen common metal ions in water, such as K⁺, Na⁺, Ca²⁺, Mg²⁺, and so forth. Furthermore, we apply the SERS sensor for real tap and lake water sample detection, and good recoveries of 113, 97, and 107% are obtained. With its advantages of high integration, simple preparation, fast response, high sensitivity, and reliability, the proposed I^--functionalized SERS sensor microfluidic chip can be a promising platform for real-time and on-site Hg²⁺ detection in natural water.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Enhancing SERS detection on a biocompatible metallic substrate for diabetes diagnosing

A method to realize surface-enhanced Raman spectroscopy (SERS) at a titanium alloy substrate for glucose detection has been experimentally demonstrated. A silver-coated laser-induced periodic surface structure (LIPSS) was prepared via femtosecond laser micro-processing. The low detection limit of glucose is 10^-7mol/L and, a good linear relationship between the glucose concentration and Raman intensity is found in the range between 1×10^-7 and 1×10^-3mol/L. Moreover, we investigate SERS detection for glucose sensing in human urine samples, while the results are in good agreement with clinical results. The Letter provides a facile method for producing a structure-controlled SERS substrate to realize glucose detection, which is promising for long-term in vivo diagnostics.

Optical glucose biosensor built-in disposable strips and wearable electronic devices

On-demand screening, real-time monitoring and rapid diagnosis of ubiquitous diseases, such as diabetes, at early stages are indispensable in personalised treatment. Emerging impacts of nano/microscale materials on optical and portable biosensor strips and devices have become increasingly important in the remarkable development of sensitive visualisation (i.e. visible inspection by the human eye) assays, low-cost analyses and personalised home testing of patients with diabetes. With the increasing public attention regarding the self-monitoring of diabetes, the development of visual readout, easy-to-use and wearable biosensors has gained considerable interest. Our comprehensive review bridges the practical assessment gap between optical bio-visualisation assays, disposable test strips, sensor array designs and full integration into flexible skin-based or contact lens devices with the on-site wireless signal transmission of glucose detection in physiological fluids. To date, the fully modulated integration of nano/microscale optical biosensors into wearable electronic devices, such as smartphones, is critical to prolong periods of indoor and outdoor clinical diagnostics. Focus should be given to the improvements of invasive, wireless and portable sensing technologies to improve the applicability and reliability of screen display, continuous monitoring, dynamic data visualisation, online acquisition and self and in-home healthcare management of patients with diabetes.

Three-dimensional porous SERS powder for sensitive liquid and gas detections fabricated by engineering dense "hot spots" on silica aerogel

A three-dimensional porous SERS powder material, Ag nanoparticles-engineered-silica aerogel, was developed. Utilizing an in situ chemical reduction strategy, Ag nanoparticles were densely assembled on porous aerogel structures, thus forming three-dimensional "hot spots" distribution with intrinsic large specific surface area and high porosity. These features can effectively enrich the analytes on the metal surface and provide huge near field enhancement. Highly sensitive and homogeneous SERS detections were achieved not only on the conventional liquid analytes but also on gas with the enhancement factor up to ∼10⁸ and relative standard deviation as small as ∼13%. Robust calibration curves were obtained from the SERS data, which demonstrates the potential for the quantification analysis. Moreover, the powder shows extraordinary SERS stability than the conventional Ag nanostructures, which makes long term storage and convenient usage feasible. With all of these advantages, the porous SERS powder material can be extended to on-site SERS "nose" applications such as liquid and gas detections for chemical analysis, environmental monitoring, and anti-terrorism.

Controlling the Morphologies of Silver Aggregates by Laser-Induced Synthesis for Optimal SERS Detection

Controlling the synthesis of metallic nanostructures for high quality surface-enhanced Raman scattering (SERS) materials has long been a central task of nanoscience and nanotechnology. In this work, silver aggregates with different surface morphologies were controllably synthesized on a glass-solution interface via a facile laser-induced reduction method. By correlating the surface morphologies with their SERS abilities, optimal parameters (laser power and irradiation time) for SERS aggregates synthesis were obtained. Importantly, the characteristics for largest near-field enhancement were identified, which are closely packed nanorice and flake structures with abundant surface roughness. These can generate numerous hot spots with huge enhancement in nanogaps and rough surface. These results provide an understanding of the correlation between morphologies and SERS performance, and could be helpful for developing optimal and applicable SERS materials.

A facile SERS strategy for quantitative analysis of trace glucose coupling glucose oxidase and nanosilver catalytic oxidation of tetramethylbenzidine

Highly stable, SERS active and catalytic nanosilver sol (AgNP) was synthesized under the exposure of light wave, using AgNO₃ as precursor and sodium citrate as reducer. Under the conditions of pH 7.0 NaH₂PO₄-Na₂HPO₄ buffer solution (PBS), the glucose can be catalyzed by glucose oxidase to produce H₂O₂ specifically. Based on the nanocatalyst and SERS substrate of AgNP, H₂O₂ can oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) quickly to form a blue oxidation product (TMB_ox) that induced the AgNPs aggregation, which exhibited a strong SERS signal at 1606 cm^-1. As the concentration of glucose increases, the TMB_ox molecular probes and AgNPs aggregation increase, and the intensity of SERS peak at 1606 cm^-1 increase linearly. Thus, a new SERS strategy for quantitative analysis of 0.33-6.67 μmol/L glucose was developed, with a detection limit of 0.035 μmol/L, coupled the catalysis of nanosilver with glucose oxidase, and label-free molecular probe of TMB_ox.

Cu@Au(Ag)/Pt nanocomposite as peroxidase mimic and application of Cu@Au/Pt in colorimetric detection of glucose and l-cysteine

Nanomaterial-based artificial peroxidase has attracted extensive interests due to their distinct advantages over natural counterpart. Cu@Au/Pt and Cu@Ag/Pt nanocomposite with rambutan-like structure were prepared and discovered to function like peroxidase, which was illustrated by catalyzing the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) accompanied with a blue color change. Steady-state investigation indicates that the catalytic kinetics of Cu@Au/Pt and Cu@Ag/Pt all followed typical Michaelis–Menten behaviors and Cu@Au/Pt showed a strong affinity for H₂O₂, while Cu@Ag/Pt showed strong affinity for TMB. The color change and absorbance intensity strongly depend on the concentration of H₂O₂, thus the direct determination of H₂O₂ and indirect detection of glucose were demonstrated using Cu@Au/Pt with a detection limit of 1.5 μM and 6 μM, respectively. What is more important, the method was applied for detection of glucose in 50% fetal bovine serum with a detection limit of 80 μM, which is much lower than the lowest glucose content in blood for diabetes (7 mM). Moreover, the Cu@Au/Pt nanocomposite were also successfully applied for sensing l-cysteine because of the inhibition effect. Considering the good peroxidase-like activity and novel structure, Cu@Au(Ag)/Pt is expected to have a wide range of applications in bioassays and biocatalysis.

Cu@Au(Ag)/Pt nanocomposite possess good peroxidase-like activity and can be used for detection of glucose and l-cysteine.

Reproducible Plasmonic Nanopyramid Array of Various Metals for Highly Sensitive Refractometric and Surface-Enhanced Raman Biosensing

Localized surface plasmon resonance (LSPR) biosensors show great potential for practical/commercial use in clinical diagnosis, home healthcare, environmental analysis, and public healthcare. However, two main issues, that is, low refractometric sensitivity and low reproducibility (large-area uniformity and batch-to-batch consistency), hinder the extensive applications of LSPR biosensors. Therefore, plasmonic nanostructures with high sensitivity and excellent reproducibility are desirable for preparing reliable LSPR sensors. Herein, we have fabricated plasmonic nanopyramid arrays (NPAs) for several batches with reproducible morphology and optical properties by elastic soft lithography and metal thermal evaporation. NPAs of various metals (i.e., Al, Au, and Ag) were also prepared by thermal evaporation with the according metals. The transmission spectra of these NPAs showed several narrow LSPR peaks in the visible-infrared wavelength region. The refractometric sensitivities of the LSPR peaks were systematically studied, and high refractometric sensitivities of 774.0, 472.8, and 421.0 nm/RIU were achieved on Al, Au, and Ag NPAs, respectively. To demonstrate the potential of the NPAs for multiplex applications, we first applied this highly sensitive Al NPA biosensor to monitoring the process of proliferation of HeLa cancer cells, in situ and in real time. Then, we demonstrated that the Au NPA was able to identify the absorbed analytes on its surface through the surface-enhanced Raman scattering spectrum. In addition, the finite difference time domain simulations were performed to reveal the electromagnetic field enhancement on NPAs. Because of the properties of high sensitivity and excellent reproducibility of the metal NPA LSPR substrates, as well as the simplicity and cost efficiency of the fabrication method, our proposed work will accelerate the practical use of LSPR sensors.

Fabrication and Characterization of a Highly-Sensitive Surface-Enhanced Raman Scattering Nanosensor for Detecting Glucose in Urine

Herein we utilized coordination interactions to prepare a novel core-shell plasmonic nanosensor for the detection of glucose. Specifically, Au nanoparticles (NPs) were strongly linked with Ag+ ions to form a sacrificial Ag shell by using 4-aminothiophenol (4-PATP) as a mediator, which served as an internal standard to decrease the influence of the surrounding on the detection. The resultant Au-PATP-Ag core-shell systems were characterized by UV-vis spectroscopy, transmission electron microscopy, and surface-enhanced Raman scattering (SERS) techniques. Experiments performed with R6G (rhodamine 6G) and CV (crystal violet) as Raman reporters demonstrated that the Au@Ag nanostructure amplified SERS signals obviously. Subsequently, the Au@Ag NPs were decorated with 4-mercaptophenylboronic acid (4-MPBA) to specifically recognize glucose by esterification, and a detection limit as low as 10⁻⁴ M was achieved. Notably, an enhanced linearity for the quantitative detection of glucose (R² = 0.995) was obtained after the normalization of the spectral peaks using 4-PATP as the internal standard. Finally, the practical applicability of the developed sensing platform was demonstrated by the detection of glucose in urine with acceptable specificity.

Electrospun CuO-Nanoparticles-Modified Polycaprolactone @Polypyrrole Fibers: An Application to Sensing Glucose in Saliva

A non-invasive method for detecting glucose is pursued by millions of diabetic patients to improve their personal management of blood glucose. In this work, a novel CuO nanoparticles (NPs) decorated polycaprolactone@polypyrrole fibers modified indium-tin oxide (denoted as CuO/PCL@PPy/ITO) electrode has been fabricated by electrospinning combined with the electrodeposition method for non-enzymatic detection of glucose in saliva fluid. The electrospun composite fibers exhibit high sensitivity for the glucose detection. The synergistic effect between CuO and PPy together with the unique three-dimensional net structure contributes the reliable selectivity, good test repeatability, large-scale production reproducibility in massive way, the reasonable stability and a high catalytic surface area to the sensor. Quantitative detection of glucose is determined in the linear range from 2 μM to 6 mM and the lowest detection limit is 0.8 μM. The CuO/PCL@PPy/ITO electrode shows potential for the non-invasive detection of salivary glucose.

A Simple and Highly Sensitive Thymine Sensor for Mercury Ion Detection Based on Surface Enhanced Raman Spectroscopy and the Mechanism Study

Mercury ion (Hg²⁺) is recognized as one of the most toxic metal ions for the environment and for human health. Techniques utilized in the detection of Hg²⁺ are an important factor. Herein, a simple thymine was successfully employed as the surface enhanced Raman spectroscopy sensor for Hg²⁺ ion detection. The limit of detection (LOD) of the developed sensor is better than 0.1 nM (0.02 ppb). This sensor can also selectively distinguish Hg²⁺ ions over 7 types of alkali, heavy metal and transition-metal ions. Moreover, the LOD of the sensor can even achieve 1 ppb in practical application in the nature system, which is half the maximum allowable level (10 nM, 2 ppb) stipulated in the US Environmental Protection Agency standard. Further investigation of the thymine-Hg²⁺-thymine coordination mechanism provides a possible means of detecting other metal ions by replacing the metal ion-specific ligands. This work paves the way for the detection of toxic metal ions and environmental problems.

Chitosan–gold nanoparticles as peroxidase mimic and their application in glucose detection in serum

Chitosan–AuNPs possess peroxidase-like activity and can be used for the detection of glucose in serum.