Spectroelectrochemical Nanosensor for the Determination of Cystatin C in Human Blood

Advancements in reusable SERS substrates for trace analysis applications

Surface Enhanced Raman Spectroscopy (SERS) technique is an effective analytical technique in which fingerprint information about analytes can be obtained, can provide detection limit performance at the single molecule level, and analyzes are performed in a single step without any intermediate steps. SERS technique offers additional benefits rather than other analytical techniques including high selectivity, ultrasensitive detection, uncomplicated protocols, in situ sampling, on-set capability and cost-effectiveness. As a result of the combination of developments in materials and nanotechnology science with the SERS analysis technique, this technique strengthens its use advantage day by day. The most important factor that limited the use of this technique was the fact that the solution containing the desired analyte(s) was dropped onto the SERS substrate and the same substrate could not be reused in subsequent analyses. To solve this problem, scientists have focused on developing reusable SERS substrates in recent years. In these studies, scientists basically used three SERS substrate cleaning applications (1) washing the SERS substrate with a suitable solvent that can elute the analyte from SERS surface after analysis, (2) cleaning the SERS substrate with catalytic degradation of analytes after analysis by modifying them with catalytic active materials and (3) Applying plasma cleaning procedure to SERS substrate after analysis and (4) applying adsorption and desorption procedure prior to SERS analysis. Herein, the aim of this review article is to evaluate the reusable SERS substrates-based methods based on their level of development and their potential to recycle. This review offers a coherent discussion on a wide range of sensing schemes employed in fabricating the SERS substrates. We utilized a critical approach in which elaborative examples were selected to highlight key shortcomings of various experimental configurations. In the same vein, there is a discussion of the advantages and limitations concerning the key instrumental advances and the expansion of the recent methods developed in this area.

Human cystatin C in fibrotic diseases

Human cystatin C (hCC), which has a pervasive distribution within body fluids and is ubiquitously expressed by numerous cells and tissues, is a highly potent extracellular inhibitor of cysteine proteases. Besides measurement of serum creatinine, which is the most widely used technique for appraising glomerular filtration rate (GFR), hCC has emerged as a relevant GFR biomarker, because its quantification in serum is less sensitive to interferences with factors such as age, muscle mass or diet. Moreover, there are growing body of evidence that hCC overexpression and/or oversecretion, which is primarily driven by TGF-β1, occur during fibrogenesis (cardiac, liver, oral, and lung fibrosis). Even though molecular mechanisms and signaling pathways governing the regulation of hCC remain to be deciphered more acutely, current data sustain that hCC expression relates to myofibrogenesis and that hCC could be a specific and valuable biomarker of fibrotic disease.

An electrochemical immunosensor for sensitive and rapid detection of cystatin C based on Fe3O4/AuNPs-MWCNTs@PDA nanocomposite

Serum Cystatin C (CysC) is an impressive marker for early diagnosis of renal dysfunction. In this work, we established a novel electrochemical immunosensor based on Fe3O4/AuNPs-MWCNTs@PDA nanocomposite for the detection of CysC. The Fe3O4/AuNPs-MWCNTs@PDA nanozyme complex by polydopamine encapsulation can not only carry massive detection antibodies, but also bind the electroactive substance toluidine blue (TB) through electrostatic adsorption. By immobilizing AuNPs onto the electrode to bind the capture antibody (Ab1), we constructed a sandwich electrochemical immunosensor with low cost, high sensitivity, and repeatability. The detection range is 3.9-125.0 ng/mL with a significant linear relationship between the current peak difference (ip) and logarithm of the CysC concentration. Moreover, the detection limit of the immunosensor is 0.157 ng/mL. We have successfully utilized this novel immunosensor to detect CysC in human serum samples, and these results have implications for its potential use in clinical application.

Advancing SERS as a quantitative technique: challenges, considerations, and correlative approaches to aid validation

Surface-enhanced Raman scattering (SERS) remains a significant area of research since it's discovery 50 years ago. The surface-based technique has been used in a wide variety of fields, most prominently in chemical detection, cellular imaging and medical diagnostics, offering high sensitivity and specificity when probing and quantifying a chosen analyte or monitoring nanoparticle uptake and accumulation. However, despite its promise, SERS is mostly confined to academic laboratories and is not recognised as a gold standard analytical technique. This is due to the variations that are observed in SERS measurements, mainly caused by poorly characterised SERS substrates, lack of universal calibration methods and uncorrelated results. To convince the wider scientific community that SERS should be a routinely used analytical technique, the field is now focusing on methods that will increase the reproducibility of the SERS signals and how to validate the results with more well-established techniques. This review explores the difficulties experienced by SERS users, the methods adopted to reduce variation and suggestions of best practices and strategies that should be adopted if one is to achieve absolute quantification.

Ultrasensitive Dual ELONA/SERS-RPA Multiplex Diagnosis of Antimicrobial Resistance

Antimicrobial resistance (AMR) is a significant global health threat concern, necessitating healthcare practitioners to accurately prescribe the most effective antimicrobial agents with correct doses to combat resistant infections. This is necessary to improve the therapeutic outcomes for patients and prevent further increase in AMR. Consequently, there is an urgent need to implement rapid and sensitive clinical diagnostic methods to identify resistant pathogenic strains and monitor the efficacy of antimicrobials. In this study, we report a novel proof-of-concept magnetic scaffold-recombinase polymerase amplification (RPA) technique, coupled with an enzyme-linked oligonucleotide assay (ELONA) and surface-enhanced Raman scattering (SERS) detection, aimed at selectively amplifying and detecting the DNA signature of three resistant carbapenemase genes, VIM, KPC, and IMP. To achieve this, streptavidin-coated magnetic beads were functionalized with biotin-modified forward primers. RPA was conducted on the surface of the beads, resulting in an immobilized duplex amplicon featuring a single overhang tail specific to each gene. These tails were subsequently hybridized with recognition HRP probes conjugated to a complementary single-stranded oligonucleotide and detected colorimetrically. Additionally, they underwent hybridization with similar selective SERS probes and were measured using a handheld Raman spectrometer. The resulting quantification limits were at subpicomolar level for both assays, allowing the potential for early diagnosis. Moreover, we demonstrated the platform capability to conduct a multiplex RPA-SERS detection of the three genes in a single tube. Compared to similar approaches like PCR, RPA offers advantages of speed, affordability, and isothermal operation at 37 °C, eliminating the need for a thermal cycler. The whole assay was completed within <2 h. Therefore, this novel magnetic scaffold ELONA/SERS-RPA platform, for DNA detection, demonstrated excellent capability for the rapid monitoring of AMR in point-of-care applications, in terms of sensitivity, portability, and speed of analysis.

Surface-Enhanced Raman Spectroscopy and Electrochemistry: The Ultimate Chemical Sensing and Manipulation Combination

One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors' sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields-energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.

Advances in uremic toxin detection and monitoring in the management of chronic kidney disease progression to end-stage renal disease

Patients with end-stage kidney disease (ESKD) rely on dialysis to remove toxins and stay alive. However, hemodialysis alone is insufficient to completely remove all/major uremic toxins, resulting in the accumulation of specific toxins over time. The complexity of uremic toxins and their varying clearance rates across different dialysis modalities poses significant challenges, and innovative approaches such as microfluidics, biomarker discovery, and point-of-care testing are being investigated. This review explores recent advances in the qualitative and quantitative analysis of uremic toxins and highlights the use of innovative methods, particularly label-mediated and label-free surface-enhanced Raman spectroscopy, primarily for qualitative detection. The ability to analyze uremic toxins can optimize hemodialysis settings for more efficient toxin removal. Integration of multiple omics disciplines will also help identify biomarkers and understand the pathogenesis of ESKD, provide deeper understanding of uremic toxin profiling, and offer insights for improving hemodialysis programs. This review also highlights the importance of early detection and improved understanding of chronic kidney disease to improve patient outcomes.

Ultrasensitive sensing urinary cystatin C via an interface-engineered graphene extended-gate field-effect transistor for non-invasive diagnosis of chronic kidney disease

Early chronic kidney disease (CKD) has strong concealment and lacks an efficient, non-invasive, and lable-free detection platform. Cystatin C (Cys C) in urine is closely related to the progress of CKD (especially at the early stage), which is an ideal endogenous marker to evaluate the impairment of renal function. Thus, the accurate detection of urinary Cys C (u-Cys C) is great significant for early prevention and treatment and delaying the course of the disease of CKD patients. Herein, we developed an extended-gate field-effect transistor (EG-FET) sensor for ultrasensitive detection of u-Cys C, which consists of a monolithic interface-engineered graphene EG electrode array and a commercially available MOSFET. Laser-induced graphene (LIG) loaded with sputtered Au NPs in the presence of adhesive Cr (Au NPs/Cr/LIG) boosts the electrical performance of the EG electrode. Meanwhile, Au NPs also serve as linkers to immobilize papain that can selectively form protein complexes with Cys C. Supported by the synergistic effect of multilevel interface-engineered graphene, our sensor exhibits a good linear correlation within the u-Cys C concentration range of 5 ag/μL to 50 ng/μL with low detection limit of 0.05 ag/μL. Our work makes accurate, specific and rapid detection of u-Cys C feasible and promising for early screening for CKD.

Application of surface-enhanced Raman spectroscopy to human serum for diagnosing liver cancer

This study investigates the application of surface-enhanced Raman spectroscopy (SERS) in the diagnosis of liver cancer using Ag@SiO2 nanoparticles as SERS substrates. A SERS test was conducted on serum samples obtained from patients with liver cancer and healthy individuals. After repeated several times experiments, it was found that the best SERS spectrum was obtained when the volume ratio of serum to deionized water was 1:2. Moreover, data preprocessing was performed on the tested SERS spectrum, and the preprocessed spectral data were combined with principal component analysis (PCA), partial least-squares discriminant analysis (PLS-DA), and orthogonal partial least squares discriminant analysis (OPLS-DA) for further analysis to classify the serum samples of patients with liver cancer and healthy individuals. The results showed that the classification effect of standard normal variate spectral data combined with the OPLS-DA was the best for the serum samples, with a classification accuracy of 97.98%, sensitivity of 97.14%, and specificity of 98.44%. Therefore, the SERS technology can be developed as a favorable method for the accurate diagnosis of liver cancer in the future.

Design and development of opto-electrochemical biosensing devices for diagnosing chronic kidney disease

Chronic kidney disease (CKD) is emerging as one of the major causes of the increase in mortality rate and is expected to become 5th major cause by 2050. Many studies have shown that it is majorly related to various risk factors, and thus becoming one of the major health issues around the globe. Early detection of renal disease lowers the overall burden of disease by preventing individuals from developing kidney impairment. Therefore, diagnosis and prevention of CKD are becoming the major challenges, and in this situation, biosensors have emerged as one of the best possible solutions. Biosensors are becoming one of the preferred choices for various diseases diagnosis as they provide simpler, cost-effective and precise methods for onsite detection. In this review, we have tried to discuss the globally developed biosensors for the detection of CKD, focusing on their design, pattern, and applicability in real samples. Two major classifications of biosensors based on transduction systems, that is, optical and electrochemical, for kidney disease have been discussed in detail. Also, the major focus is given to clinical biomarkers such as albumin, creatinine, and others related to kidney dysfunction. Furthermore, the globally developed sensors for the detection of CKD are discussed in tabulated form comparing their analytical performance, response time, specificity as well as performance in biological fluids.

Application of SERS-based nanobiosensors to metabolite biomarkers of CKD

A clinical diagnosis of chronic kidney disease (CKD) is commonly achieved by estimating the serum levels of urea and creatinine (CR). Given the limitations of the conventional diagnostic assays, it is imperative to seek alternative, economical strategies for the detection of CKD-specific biomarkers with high specificity and selectivity. In this respect, surface-enhanced Raman spectroscopy (SERS) can be regarded as an ideal choice. SERS signals can be greatly amplified by noble metal nanoparticles (e.g., gold nanoparticles (GNPs)) of numerous sizes, shapes, and configurations to help achieve ultra-sensitive single molecule-level detection at 10^-15 M (up to 10 orders of magnitude more sensitive than fluorescence-based detection). The irregular geometry of GNPs with spike-like tips, dimers, and aggregates with small nanogaps (i.e., due to plasmon coupling such as Raman hot spots) play a pivotal role in enhancing the specificity and sensitivity of SERS. This review critically outlines the performance of SERS-based biosensors in the ultrasensitive detection of CKD biomarkers in various body fluids in terms of basic quality assurance parameters (e.g., limit of detection, figure of merit, enhancement factor, and stability of the biosensor). Moreover, the challenges and perspectives are described with respect to the expansion of such sensing techniques in practical clinical settings.

Toward a New Era of SERS and TERS at the Nanometer Scale: From Fundamentals to Innovative Applications

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) have opened a variety of exciting research fields. However, although a vast number of applications have been proposed since the two techniques were first reported, none has been applied to real practical use. This calls for an update in the recent fundamental and application studies of SERS and TERS. Thus, the goals and scope of this review are to report new directions and perspectives of SERS and TERS, mainly from the viewpoint of combining their mechanism and application studies. Regarding the recent progress in SERS and TERS, this review discusses four main topics: (1) nanometer to subnanometer plasmonic hotspots for SERS; (2) Ångström resolved TERS; (3) chemical mechanisms, i.e., charge-transfer mechanism of SERS and semiconductor-enhanced Raman scattering; and (4) the creation of a strong bridge between the mechanism studies and applications.

Towards Label-free detection of viral disease agents through their cell surface proteins: Rapid screening SARS-CoV-2 in biological specimens

Current methods for the screening of viral infections in clinical settings, such as reverse transcription polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), are expensive, time-consuming, require trained personnel and sophisticated instruments. Therefore, novel sensors that can save time and cost are required specially in remote areas and developing countries that may lack the advanced scientific infrastructure for this task. In this work, we present a sensitive, and highly specific biosensing approach for the detection of harmful viruses that have cysteine residues within the structure of their cell surface proteins. We utilized new method for the rapid screening of SARS-CoV-2 virus in biological fluids through its S1 protein by surface enhanced Raman spectroscopy (SERS). The protein is captured from aqueous solutions and biological specimens using a target-specific extractor substrate. The structure of the purified protein is then modified to convert it into a bio-thiol by breaking the disulfide bonds and freeing up the sulfhydryl (SH) groups of the cysteine residues. The formed biothiol chemisorbs favourably onto a highly sensitive plasmonic sensor and probed by a handheld Raman device in few seconds. The new method was used to screen the S1 protein in aqueous medium, spiked human blood plasma, mucus, and saliva samples down to 150 fg/L. The label-free SERS biosensing method has strong potential for the fingerprint identification many viruses (e.g. the human immunodeficiency virus, the human polyomavirus, the human papilloma virus, the adeno associated viruses, the enteroviruses) through the cysteine residues of their capsid proteins. The new method can be applied at points of care (POC) in remote areas and developing countries lacking sophisticated scientific infrastructure.

Review on combining surface-enhanced Raman spectroscopy and electrochemistry for analytical applications

The discovery of surface enhanced Raman scattering (SERS) from an electrochemical (EC)-SERS experiment is known as a historic breakthrough. Five decades have passed and Raman spectroelectrochemistry (SEC) has developed into a common characterization tool that provides information about the electrode-electrolyte interface. Recently, this technique has been successfully explored for analytical purposes. EC was found to highly improve the performances of SERS sensors, providing, among others, controlled adsorption of analytes and increased reproducibility. In this review, we highlight the potential of EC-SERS sensors to be implemented for point-of-need (PON) analyses as miniaturized devices, and their ability to revolutionize fields like quality control, diagnosis or environmental and food safety. Important developments have been achieved in Raman spectroelectrochemistry, which now represents a promising alternative to conventional analytical methods and interests more and more researchers. The studies included in this review open endless possibilities for real-life EC-SERS analytical applications.

Advances in Biosensor Technologies for Acute Kidney Injury

Acute kidney injury (AKI) is one of the most prevalent and complex clinical syndromes with high morbidity and mortality. The traditional diagnosis parameters are insufficient regarding specificity and sensitivity, and therefore, novel biomarkers and their facile and rapid applications are being sought to improve the diagnostic procedures. The biosensors, which are employed on the basis of electrochemistry, plasmonics, molecular probes, and nanoparticles, are the prominent ways of developing point-of-care devices, along with the mutual integration of efficient surface chemistry strategies. In this manner, biosensing platforms hold pivotal significance in detecting and quantifying novel AKI biomarkers to improve diagnostic interventions, potentially accelerating clinical management to control the injury in a timely manner. In this review, novel diagnostic platforms and their manufacturing processes are presented comprehensively. Furthermore, strategies to boost their effectiveness are also indicated with several applications. To maximize these efforts, we also review various biosensing approaches with a number of biorecognition elements (e.g., antibodies, aptamers, and molecular imprinting molecules), as well as benchmark their features such as robustness, stability, and specificity of these platforms.

Label-free identification of Erythropoietin isoforms by surface enhanced Raman spectroscopy

We present a sensitive label-free surface enhanced Raman spectroscopy (SERS) method for the discrimination between the recombinant and endogenous human Erythropoietin (EPO) isoforms. The proposed methodology comprises a lectin-functionalised extractor chip for the extraction of the recombinant human EPO (rhuEPO) and the endogenous EPO (enEPO) from blood plasma. The disulfide bond molecular structure of the purified isoforms was modified to chemisorb the biomolecules onto a SERS substrate in a unified orientation, thus maximizing the reproducibility and sensitivity of the SERS measurements. The acquired SERS spectra of the EPO isoforms showed diagnostic Raman bands that allowed for the discrimination between rhuEPO and enEPO. The method was also used for the SERS quantification of rhuEPO and enEPO down to 0.1 pM and 0.5 pM, respectively. The SERS determination of the protein isoforms was cross validated against ELISA. The new SERS method has strong potential for the rapid screening of rhuEPO doping in athletes and for the therapeutic drug monitoring of rhuEPO treatment in cancer patients.

Rapid ultra-sensitive diagnosis of clostridium difficile infection using a SERS-based lateral flow assay

Clostridium difficile (C. diff) infection is one of the most contagious diseases associated with high morbidity and mortality rates in hospitalised patients. Accurate diagnosis can slow its spread by determining the most effective treatment. Herein, we report a novel testing platform as a proof-of-concept for the selective, sensitive, rapid and cost-effective diagnosis of C. diff infection (CDI) based on a duplex measurement. This was achieved by detecting two specific biomarkers, surface layer protein A (SlpA) and toxin B (ToxB), using a surface enhanced Raman scattering-based lateral flow assay (SERS-based LFA). The simultaneous duplex detection of SlpA with ToxB has not been described for the clinical diagnosis of CDI previously. The SlpA biomarker "AKDGSTKEDQLVDALA" was first reported by our group in 2018 as a species-specific identification tool. The second biomarker, ToxB, is the essential virulence biomarker of C. diff pathogenic strains and is required to confirm true infection pathogenicity. The proposed SERS-based LFA platform enabled rapid duplex detection of SlpA and ToxB on separate test lines using a duplex LF test strip within 20 minutes. The use of a handheld Raman spectrometer to scan test lines allowed for the highly sensitive quantitative detection of both biomarkers with a lowest observable concentration of 0.01 pg μL-1. The use of a handheld device in this SERS-based LFA instead of benchtop machine paves the way for rapid, selective, sensitive and cheap clinical evaluation of CDI at the point of care (POC) with minimal sample backlog.

Plastic Antibody of Polypyrrole/Multiwall Carbon Nanotubes on Screen-Printed Electrodes for Cystatin C Detection

This work reports the design of a novel plastic antibody for cystatin C (Cys-C), an acute kidney injury biomarker, and its application in point-of-care (PoC) testing. The synthetic antibody was obtained by tailoring a molecularly imprinted polymer (MIP) on a carbon screen-printed electrode (SPE). The MIP was obtained by electropolymerizing pyrrole (Py) with carboxylated Py (Py-COOH) in the presence of Cys-C and multiwall carbon nanotubes (MWCNTs). Cys-C was removed from the molecularly imprinted poly(Py) matrix (MPPy) by urea treatment. As a control, a non-imprinted poly(Py) matrix (NPPy) was obtained by the same procedure, but without Cys-C. The assembly of the MIP material was evaluated in situ by Raman spectroscopy and the binding ability of Cys-C was evaluated by the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) electrochemical techniques. The MIP sensor responses were measured by the DPV anodic peaks obtained in the presence of ferro/ferricyanide. The peak currents decreased linearly from 0.5 to 20.0 ng/mL of Cys-C at each 20 min successive incubation and a limit of detection below 0.5 ng/mL was obtained at pH 6.0. The MPPy/SPE was used to analyze Cys-C in spiked serum samples, showing recoveries <3%. This device showed promising features in terms of simplicity, cost and sensitivity for acute kidney injury diagnosis at the point of care.

Rapid and selective detection of recombinant human erythropoietin in human blood plasma by a sensitive optical sensor

Recombinant human erythropoietin (rHuEPO) is an important hormone drug that is used to treat several medical conditions. It is also frequently abused by athletes as a performance enhancing agent at sporting events. The time window of the rHuEPO in blood is short. Therefore, the rapid detection of rHuEPO use/abuse at points of care and in sports requires a selective analytical method and a sensitive sensor. Herein, we present a highly selective method for the rapid detection of rHuEPO in human blood plasma by a sensitive optical sensor. rHuEPO is selectively extracted from human blood plasma by a target-specific extractor chip and converted into a biothiol by reducing its disulfide bond structure. The formed biothiol reacts with a water soluble (E)-1-((6-methoxybenzo[d]thiazole-2-yl)diazenyl)naphthalene-2,6-diolHg(ii) (BAN-Hg) optical sensor and causes its rapid decomposition. This leads to a rapid change in the sensor color from blue to pink that can be observed by the naked eye. The optical sensor was used to quantify rHuEPO in the concentration range 1 × 10-8 M to 1 × 10-12 M by UV-Vis spectroscopy. For the screening of blood plasma, an EPO-specific extractor chip was synthesized and used to selectively extract the protein from the biological matrix prior to its conversion into biothiol and quantification by the optical sensor. Since many proteins have a disulfide bond structure, the new method has strong potential for their rapid sensitive and selective detection by the BAN-Hg sensor and UV-Vis spectroscopy.

Hierarchical Plasmonic-Fluorescent Labels for Highly Sensitive Lateral Flow Immunoassay with Flexible Dual-Modal Switching

Lateral flow immunoassay (LFIA), as a prominent point-of-care (POC) test platform, has been extensively adopted for rapid, on-site, and facile diagnosis of pathogen infections and disease biomarkers. Exploring novel structured optical labels of LFIA with amplified signal and complementary detection modes favors the sensitive and flexible POC diagnosis. Here, bimodal labels with both colorimetric and fluorescent readout were fabricated via a layered sequential assembly strategy based on affinity templates and hydrophobic metal-containing nanounits. High-quality colorimetric and fluorescent nanoparticles were densely incorporated into the colloidal supports and confined in separated regions, without interfering with each other. The hierarchical integration of gold nanoparticles and quantum dots with high loading density and good optical preservation realized dual readout and amplified signals from the assemblies of individual single nanoparticles. The "all-in-one" optical labels allowed both colorimetric and fluorescent detection of cystatin C (Cys C) after surface conjugation with antibodies. The LFIA strips revealed noninterfering dual signals for both visual inspection and quantitative detection of Cys C via the naked eye and portable devices, respectively. The limits of detection by colorimetric and fluorescent modes were 0.61 and 0.24 ng mL^-1, respectively. The novel LFIA platform demonstrated sensitive, specific, and reproducible POC testing of biomarkers with flexible detection modes and was reliable for clinical diagnosis.

SERS-based magnetic immunoassay for simultaneous detection of cTnI and H-FABP using core-shell nanotags

Acute myocardial infarction (AMI) is the single leading cause of worldwide mortality and morbidity. Heart-type fatty acid-binding protein (H-FABP) and cardiac troponin I (cTnI), as biomarkers emerging at different stages of AMI, have complementary advantages in terms of specificity and sensitivity. Therefore, we developed a magnetic immunoassay method based on surface-enhanced Raman scattering (SERS) to detect H-FABP and cTnI simultaneously. Herein, two mutually independent Raman reporter molecules were embedded between a gold core and silver shell and then combined with a tracer antibody to form a SERS immunoprobe. During detection, the SERS immunoprobe, target antigen and capture probe undergo an immune reaction to form a sandwich structure, and then the immune complex was enriched by a specific reaction of streptavidin on the surface of magnetic beads with biotin. Finally, the concentration of biomarkers was quantified by detecting the characteristic Raman peak intensities of the two Raman reporter molecules. Under the optimized conditions, the minimum detection limits of H-FABP and cTnI were 0.6396 and 0.0044 ng mL^-1, respectively. Besides, the target antigen does not cross-react with non-specific proteins, showing good specificity. Therefore, our proposed SERS-based magnetic immunoassay method has the advantages of accuracy, rapidity and good selectivity, and has great potential for early diagnosis of acute myocardial infarction disease.

Nanophotonic-Carbohydrate Lab-on-a-Microneedle for Rapid Detection of Human Cystatin C in Finger-Prick Blood

Miniaturized total analysis systems, for the rapid detection of disease biomarkers, with features including high biomarker sensitivity, selectivity, biocompatibility, and disposability, all at low cost are of profound importance in the healthcare sector. Within this frame of reference, we developed a lab-on-a-carbohydrate-microneedle biodevice by integrating localized surface plasmon resonance (LSPR) paper-based substrates with biocompatible microneedles of high aspect ratio (>60:1 length:width). These microneedles are completely fabricated with carbohydrate (maltose) and further coated with poly lactic-co-glycolic acid (PLGA), which together serves the purpose of fluid channels. The porous nature of PLGA, in addition to drawing blood by capillary action, filters out the whole blood, allowing only the blood plasma to reach the biorecognition layer of the developed biodevice. While the use of maltose provides biocompatibility to the microneedle, the axial compression and transverse load analysis revealed desired mechanical strength of the microneedle, with mechanical failure occurring at 11N and 9 N respectively for the compressive and transverse load. For a proof-of-principle demonstration, the developed biodevice is validated for its operational features by direct detection of cystatin C in finger-prick blood and up to a concentration of 0.01 μg/mL in buffered conditions using the LSPR technique. Furthermore, by changing the biorecognition layer, the use of the developed needle can be extended to other disease biomarkers, and therefore the innovation presented in this work represents a hallmark in the state of the art of lab-on-a-chip biodevices.

Gold-Deposited Nickel Foam as Recyclable Plasmonic Sensor for Therapeutic Drug Monitoring in Blood by Surface-Enhanced Raman Spectroscopy

A sensitive and recyclable plasmonic nickel foam sensor has been developed for surface-enhanced Raman spectroscopy (SERS). A simple electrochemical method was used to deposit flower-shaped gold nanostructures onto nickel foam substrate. The high packing of the gold nanoflowers onto the nickel foam led to a high enhancement factor (EF) of 1.6 × 10¹¹. The new SERS sensor was utilized for the direct determination of the broad-spectrum β-lactam carbapenem antibiotic meropenem in human blood plasma down to one pM. The sensor was also used in High Performance Liquid Chromatography (HPLC)-SERS assembly to provide fingerprint identification of meropenem in human blood plasma. Moreover, the SERS measurements were reproducible in aqueous solution and human blood plasma (RSD = 5.5%) and (RSD = 2.86%), respectively at 200 µg/mL (n = 3), and successfully recycled using a simple method, and hence, used for the repeated determination of the drug by SERS. Therefore, the new sensor has a strong potential to be applied for the therapeutic drug monitoring of meropenem at points of care and intensive care units.

Homogenous Magneto-Fluorescent Nanosensor for Tumor-Derived Exosome Isolation and Analysis

Tumor-derived exosomes carrying unique surface proteins have shown great promise as novel biomarkers for liquid biopsies. However, point-of-care analysis for tumor-derived exosomes in the blood with low-cost and easy processing is still challenging. Herein, we develop an integrated approach, homogenous magneto-fluorescent exosome (hMFEX) nanosensor, for rapid and on-site tumor-derived exosomes analysis. Tumor-derived exosomes are captured immunomagnetically, which further initiates the aptamer-triggered assembly of DNA three-way junctions in homogenous solution containing aggregation-induced emission luminogens and graphene oxide, resulting in an amplified fluorescence signal. By integrating magnetic isolation and enhanced fluorescence measurement, the hMFEX nanosensor detects tumor-derived exosomes in the dynamic range spanning 5 orders of magnitude with high specificity, and the limit of detection is 6.56 × 10⁴ particles/μL. Analyzing tumor-derived exosomes in limited volume plasma from breast cancer patients demonstrates the excellent clinical diagnostic efficacy of the hMFEX nanosensor. This study provides new insights into the point-of-care testing of tumor-derived exosomes for cancer diagnostics.

A SERS quenching method for the sensitive determination of insulin

In this work, we utilise the disulphide bond structure of insulin and a new benzothiazole Raman probe for the detection of human insulin using surface-enhanced Raman spectroscopy (SERS). The disulphide bond structure of the insulin was reduced to generate free sulfhydryl terminal groups. When reacted with benzothiazole-functionalised gold nanoparticles, the reduced protein desorbs the Raman probe and causes its Raman signal intensity to quench. Using this approach, insulin was quantified in the concentration range of 1 × 10^-14 -1 × 10^-8 M by SERS quenching. The limit of quantification of insulin by the SERS quenching method was found to be 1 × 10^-14 M (0.01 pM or 58 pg/L), which satisfies the requirements for monitoring its blood concentration in patients. Because many proteins and peptides have disulphide bonds in their molecular structures, the new SERS quenching method has a strong potential for the rapid determination of ultralow concentrations of proteins in formulations and biological fluids.

Toward Label-Free SERS Detection of Proteins through Their Disulfide Bond Structure

The molecular structure of many proteins contains disulfide bonds between their cysteine residues. In this work we demonstrate the utilization of the disulfide bond structure of proteins for their label-free determination by surface-enhanced Raman spectroscopy (SERS). The new approach for label-free SERS detection of proteins is demonstrated for human insulin. The protein was selectively extracted from spiked plasma samples using target-specific functionalized nanomaterial. Enzyme-linked immune assay (ELISA) was used to detect insulin in the blood plasma and cross-validate the SERS method. The disulfide bonds in the molecular structure of the protein were chemically reduced and used for their chemisorption onto the gold-coated copper oxide substrate in a unified orientation at a very short distance from the hotspots. The oriented chemisorption of the protein caused significant enhancement to the signal intensity of its Raman vibration modes. This is attributed to the strong short-range electromagnetic and chemical enhancement effects that are experienced by the immobilized protein. Using this approach, label-free and reproducible SERS detection of insulin, down to 10 zM (relative standard deviation [RSD] = 5.52%), was achieved. Sixty-five percent of proteins contain disulfide bonds in their molecular structure. Therefore, the new label-free SERS detection method has strong potential for the determination of ultralow concentrations of proteins at pathology labs and in biology research.