A simple aptamer-based colorimetric assay for rapid detection of C-reactive protein using gold nanoparticles

Integrated biosensor array for multiplex biomarkers cancer diagnosis via in-situ self-assembly carbon nanotubes with an ordered inverse-opal structure

To enhance the precision and reliability of early disease detection, especially in malignancies, an exhaustive investigation of multi-target biomarkers is essential. In this study, an advanced integrated electrochemical biosensor array that demonstrates exceptional performance was constructed. This biosensor was developed through a controllable porous-size mechanism and in-situ modification of carbon nanotubes (CNTs) to quantify multiplex biomarkers-specifically, C-reaction protein (CRP), carbohydrate antigen 125 (CA125), and carcinoembryonic antigen (CEA)-in human serum plasma. The fabrication process involved creating a highly ordered three-dimensional inverse-opal structure with the CNTs (pCNTs) modifier through microdroplet-based microfluidics, confined spatial self-assembly of nanoparticles, and chemical wet-etching. This innovative approach allowed for direct in-situ modification of nanomaterial onto the surface of electrode array, eliminating secondary transfer and providing exceptional control over structure and stability. The outstanding electrochemical performance was achieved through the synergistic effect of the pCNTs nanomaterial, aptamer, and horseradish peroxidase-labeled (HRP-) antibody. Additionally, the integrated biosensor array platform comprised multiple individually addressable electrode units (n = 11), enabling simultaneous multi-parallel/target testing, thereby ensuring accuracy and high throughput. Crucially, this integrated biosensor array accurately quantified multiplex biomarkers in human serum, yielding results comparable to commercial methods. This integrated technology holds promise for point-of-care testing (POCT) in early disease diagnosis and biological analysis.

Gold nanoparticles-based biosensors: pioneering solutions for bacterial and viral pathogen detection-a comprehensive review

Gold Nanoparticles (AuNPs) have gained significant attention in biosensor development due to their unique physical, chemical, and optical properties. When incorporated into biosensors, AuNPs offer several advantages, including a high surface area-to-volume ratio, excellent biocompatibility, ease of functionalization, and tunable optical properties. These properties make them ideal for the detection of various biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Traditional methods for detecting bacteria and viruses, such as RT-PCR and ELISA, often suffer from complexities, time consumption, and labor intensiveness. Consequently, researchers are continuously exploring novel devices to address these limitations and effectively detect a diverse array of infectious pathogenic microorganisms. In light of these challenges, nanotechnology has been instrumental in refining the architecture and performance of biosensors. By leveraging advancements in nanomaterials and strategies of biosensor fabrication the sensitivity and specificity of biosensors can be enhanced, enabling more precise detection of pathogenic bacteria and viruses. This review explores the versatility of AuNPs in detecting a variety of biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Furthermore, it evaluates recent advancements in AuNPs-based biosensors for the detection of pathogens, utilizing techniques such as optical biosensors, lateral flow immunoassays, colorimetric immunosensors, electrochemical biosensors, and fluorescence nanobiosensors. Additionally, the study discusses the existing challenges in the field and proposes future directions to improve AuNPs-based biosensors, with a focus on enhancing sensitivity, selectivity, and their utility in clinical and diagnostic applications.

Aptamer-conjugated gold nanoparticles for portable, ultrasensitive naked-eye detection of C-reactive protein based on the Tyndall effect

BACKGROUND

C-reactive protein (CRP) represents an early clinical biomarker that indicates the presence of inflammatory or infectious conditions in the human body. Today's procedures approved by the Food and Drug Administration (FDA) imply expensive equipment and highly trained personnel to perform the test. Therefore, a new diagnostic method with high detection efficiency and less cost is urgently needed for delivering rapid and timely results in point-of-care (POC) service.

RESULTS

Herein, we propose a new, equipment-free, and portable sensing method for the future POC detection of CRP based on the Tyndall effect (TE). In our study, aptamer-conjugated citrate-stabilized gold nanoparticles (apta-AuNPs) are exploited as the sensing platform. The apta-AuNPs' interaction with CRP in a saline environment leads to their aggregation, thus enhancing the scattering of light when the solution is exposed to a 640 nm pointer laser line. Firstly, the enhancement of the scattering light as a function of increasing concentration of CRP in solution is measured spectroscopically using a typical 90-degree angle spectrofluorometer and then the measurements are compared to the classic colorimetric detection using an UV-Vis spectrophotometer. Finally, to achieve high portability and accessibility, we demonstrate that the measurement of CRP concentration can be performed with similar accuracy but in a more direct and inexpensive way by using a laser pointer pen as the excitation source and a camera of a low-budget smartphone as a quantitative reader instead of most expensive spectrofluorometer.

SIGNIFICANCE

The portable TE-based assay exhibits a wide linear dynamic range (1-60 μg/mL) for the detection of CRP with a limit of detection (LOD) of 92 ng/mL The proposed method is capable to integrate both standard and high-sensitivity CRP analysis in a single procedure with increased sensitivity and prompt delivery of analysis results. Moreover, the sensing procedure is significantly faster than the FDA approved ones with a detection time of only 10 min. Finally, as a proof-of-concept, our findings demonstrate excellent recovery for CRP detection in spiked and diluted urine samples, highlighting the strong potential of this sensing method for POC applications.

Multiplex signal amplification for ultrasensitive CRP assay via integrated electrochemical biosensor array using MOF-derived carbon material and aptamers

Accurate and precise detection of disease-associated proteins, such as C-reactive protein (CRP), remains a challenge in biosensor development. Herein, we present a novel approach－an integrated disposable aptasensor array－designed for precise, ultra-sensitive, and parallel detection of CRP in plasma samples. This integrated biosensing array platform enables multiplex parallel testing, ensuring the accuracy and reliability in sample analysis. The ultra-sensitivity of this biosensor is achieved through multiplex signal amplification. Leveraging the superior conductivity and extensive surface area of MOF-derived nanoporous carbon material (CMOF), the biosensor enhances recognition elements (aptamers) by catalyzing the horseradish peroxidase (HRP) label enzyme reaction to multiply the number of probe molecules. Optimized conditions yielded exceptional performance, exhibiting high accuracy (relative standard deviation, RSD≤10.0 %), a low detection limit (0.3 pg/mL, S/N = 3), ultra-sensitivity (0.16 μA/ng mL-1 mm-2), and a rapid response (seven parallel tests within 60 min). Importantly, this multi-unit integrated disposable aptasensor array accurately quantified CRP in human serum, demonstrating comparable results to commercial enzyme-linked immunosorbent assay (ELISA). This technology showcases promise for detecting various biomarkers using a unified approach, presenting an appealing strategy for early disease diagnosis and biological analysis.

Development and performance of NLISA for C-reactive protein detection based on Prussian blue nanoparticle conjugates

Prussian blue nanoparticles (PBNPs), also called nanozymes, are very attractive as an alternative to horseradish peroxidase in immunoassay development due to their simple and low-cost synthesis, stability and high catalytic activity. Today, there is a method for highly effective PBNP synthesis based on the reduction of an FeCl3/K3[Fe(CN)6] mixture by hydrogen peroxide. However, there is a lack of research showcasing the use of these highly effective PBNPs for specific target detection in clinical settings, as well as a lack of comprehensive comparisons with conventional methods. To address this gap, we prepared diagnostic reagents based on highly effective PBNPs by modifying them using gelatin and attaching anti-C-reactive protein (CRP) monoclonal antibodies through cross-linking with glutaraldehyde. As a result, a solid-phase colorimetric immunoassay in a sandwich format (nanozyme-linked immunosorbent assay [NLISA]) using highly effective PBNPs as a label for CRP detection has been demonstrated for the first time. The assay demonstrated a detection limit of 21.8 pg/mL, along with acceptable selectivity, precision (CV < 25%) and accuracy (the recovery index was within acceptable limits (75-125%) for LLOQ /ULOQ range. The analytical performance of this method is on par with sensitive assays developed in the last 5 years. Notably, the results obtained from NLISA align with those from an immunofluorescence assay conducted by a certified clinical laboratory. Furthermore, this study underscores the technological challenges involved in constructing an analysis that necessitate further exploration.

Aptamers and Nanobodies as New Bioprobes for SARS-CoV-2 Diagnostic and Therapeutic System Applications

The global challenges posed by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic have underscored the critical importance of innovative and efficient control systems for addressing future pandemics. The most effective way to control the pandemic is to rapidly suppress the spread of the virus through early detection using a rapid, accurate, and easy-to-use diagnostic platform. In biosensors that use bioprobes, the binding affinity of molecular recognition elements (MREs) is the primary factor determining the dynamic range of the sensing platform. Furthermore, the sensitivity relies mainly on bioprobe quality with sufficient functionality. This comprehensive review investigates aptamers and nanobodies recently developed as advanced MREs for SARS-CoV-2 diagnostic and therapeutic applications. These bioprobes might be integrated into organic bioelectronic materials and devices, with promising enhanced sensitivity and specificity. This review offers valuable insights into advancing biosensing technologies for infectious disease diagnosis and treatment using aptamers and nanobodies as new bioprobes.

Wearing the Lab: Advances and Challenges in Skin-Interfaced Systems for Continuous Biochemical Sensing

Continuous, on-demand, and, most importantly, contextual data regarding individual biomarker concentrations exemplify the holy grail for personalized health and performance monitoring. This is well-illustrated for continuous glucose monitoring, which has drastically improved outcomes and quality of life for diabetic patients over the past 2 decades. Recent advances in wearable biosensing technologies (biorecognition elements, transduction mechanisms, materials, and integration schemes) have begun to make monitoring of other clinically relevant analytes a reality via minimally invasive skin-interfaced devices. However, several challenges concerning sensitivity, specificity, calibration, sensor longevity, and overall device lifetime must be addressed before these systems can be made commercially viable. In this chapter, a logical framework for developing a wearable skin-interfaced device for a desired application is proposed with careful consideration of the feasibility of monitoring certain analytes in sweat and interstitial fluid and the current development of the tools available to do so. Specifically, we focus on recent advancements in the engineering of biorecognition elements, the development of more robust signal transduction mechanisms, and novel integration schemes that allow for continuous quantitative analysis. Furthermore, we highlight the most compelling and promising prospects in the field of wearable biosensing and the challenges that remain in translating these technologies into useful products for disease management and for optimizing human performance.

Development of antibody-aptamer sandwich-like immunosensor based on RCA and Nicked-PAM CRISPR/Cas12a system for the ultra-sensitive detection of a biomarker

Biomarkers are the most sensitive reactants and early indicators of many kinds of diseases. The development of highly sensitive and simple techniques to quantify them is challenging. In this study, based on rolling cycle amplification (RCA) and the Nicked PAM/CRISPR-Cas12a system (RNPC) as a signal reporter, a sandwich-type method was developed using antibody@magnetic beads and aptamer for the high-sensitive detection of the C-reactive protein (CRP). The antibody-antigen (target)-aptamer sandwich-like reaction was coupled to RCA, which can produce hundreds of similar binding sites and are discriminated by CRISPR/Cas12a for signal amplification. The ultrasensitivity is achieved based on the dual-signal enhancing strategy, which involves the special recognition of aptamers, RCA, and trans-cleavage of CRISPR/Cas12a. By incorporating the CRISPR/Cas12a system with cleaved PAM, the nonspecific amplification of the RCA reaction alone was greatly reduced, and the dual signal output of RCA and Cas12a improved the detection sensitivity. Our assay can be performed only in two steps. The first step takes only 20 min of target capture, followed by a one-pot reaction, where the target concentration can be obtained by fluorescence values as long as there are 37 °C reaction conditions. Under optimal conditions, this system detected CRP with high sensitivity. The fabricated biosensor showed detection limits of 0.40 pg/mL in phosphate-buffered saline and 0.73 pg/mL in diluted human serum and a broad linear dynamic range of 1.28 pg/mL to 100 ng/mL within a total readout time of 90 min. The method could be used to perform multi-step signal amplification, which can help in the ultrasensitive detection of other proteins. Overall, the proposed biosensor might be used as an immunosensor biosensor platform.

Colorimetric analysis of C-reactive protein via 'jellyfish' probe-based exonuclease III-assisted multiple-signal recycles

C-reactive protein (CRP) is a potential biomarker for evaluating inflammatory responses in patients receiving coronary artery bypass graft surgery. Here, the authors depict a sensitive and reliable colorimetric approach for CRP analysis. In this method, an aptamer specifically binds with CRP and an initiator sequence is released from an arch probe to activate signal amplification. The released initiator sequence hybridizes with the toehold section in the 'jellyfish' probe to form a blunt terminus to induce exonuclease III-assisted signal amplification. The method exhibited a low limit of detection of 1.32 ng/ml and high intraday and interday precision for CRP detection. In summary, this colorimetric approach may provide a potential alternative tool for the evaluation of inflammation in patients receiving coronary artery bypass graft and clinical diagnostics of disease.

Cobalt oxide modified sulfur and phosphorus Co-doped g-C3N4 for screening of urinary human albumin

The fabrication of a heteroatom-doped nanocomposite based on cobalt oxide modified sulfur, phosphorus co-doped carbon nitride (Co3O4/SP-CN) with increased active sites is reported. The synthesized nanocomposite offers surprisingly high electrocatalytic oxidation efficacy toward human albumin (HA) despite its agglomeration. This improved efficacy of Co3O4/SP-CN nanocomposite could be attributed to its increased adsorption sites and surface defects, fast charge transportation capability, and conductivity. Additionally, morphological and compositional analysis of the fabricated Co3O4/SP-CN material has been performed  through scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photon spectroscopy (XPS), and Raman spectroscopy. The fabricated electrode shows remarkable amperometric response against the HA with a limit of detection of 8.39 nM and linear range of 20-4000 nM at applied potential of 0.25 V versus Ag/AgCl in 0.1 M PBS (pH 8.2). The designed Co3O4/SP-CN electrode has been successfully applied to monitor HA in  urine samples of diabetic patient with recovery percentage from 94.1 and 92.1% and with relative standard deviation (RSD) values of 5.8 and 7.8%. According to the best of our knowledge, this is the first report to use a Co3O4/SP-CN-based graphitic pencil (GP) electrode for monitoring of HA for early diagnosis of diabetic nephropathy.

Low-Cost Full-Range Detection of C-Reactive Protein in Clinical Samples by Aptamer Hairpin Probes and Coprecipitation of Silver Ions and Gold Nanoparticles

C-reactive protein (CRP) levels can vary widely related to diverse disease contexts. However, expensive antibodies have impeded the clinical utility of antibody-based full-range CRP assays, especially in developing countries. Herein, we established a low-cost, antibody-free, 96-well plate-based full-range CRP detection method by combining gold nanoparticles (AuNPs), silver iodide (AgI), Eosin Y, and the aptamer hairpin probe (AHP) with Ag+-mediated cytosine-cytosine mismatches, that is, the Au@AgI/Eosin Y-AHP method. After binding the target CRP, the AHP released Ag+, which subsequently induced the aggregation of AuNPs on the surface of AgI colloids, resulting in a significant increase in the adsorption of Eosin Y on the surface of AuNPs. The changes in fluorescence intensity (FI) of Eosin Y in the supernate without and with CRP were proportional to the concentration of the CRP in the wide range of 0.01-40 ng/mL (r = 0.9969), and 96 samples can be detected in 96-well plates simultaneously by a microplate reader within 45 min. Remarkably, the CRP levels of 100 clinical samples achieved with the Au@AgI/Eosin Y-AHP had a good correlation with those obtained with the latex-enhanced immune turbidimetry assay (r = 0.986). Furthermore, the kit based on the Au@AgI/Eosin Y-AHP method costs only $8.1 for 100 tests. Therefore, the new method is beneficial for less developed areas where expensive assays are not affordable.

Nano techniques: an updated review focused on anthocyanin stability

Anthocyanins (ACNs) are one of the subgroups of flavonoids and getting intensive attraction due to the nutritional values. However, their application of ACNs is limited due to their poor stability and bioavailability. Accordingly, nanoencapsulation has been developed to enhance its stability and bio-efficacy. This review focuses on the nano-technique applications of delivery systems that be used for ACNs stabilization, with an emphasis on physicochemical stability and health benefits. ACNs incorporated with delivery systems in forms of nano-particles and fibrils can achieve advanced functions, such as improved stability, enhanced bioavailability, and controlled release. Also, the toxicological evaluation of nano delivery systems is summarized. Additionally, this review summarizes the challenges and suggests the further perspectives for the further application of ACNs delivery systems in food and medical fields.

LSPR-Based Aptasensor for Rapid Urinary Detection of NT-proBNP

N-terminal pro-brain natriuretic peptide (NT-proBNP) is a myocardial stress biomarker that can be found in serum or plasma, saliva, and urine in the context of cardiovascular disease. In this study, we developed a rapid (~25 min) and straightforward localized surface plasmon resonance (LSPR)-based assay for detecting NT-proBNP in urine. The assay employs citrate-capped gold nanoparticles (AuNPs) and an aptamer specific for NT-proBNP, which initially interacts with NT-proBNP. The remaining unbound aptamer then interacts with the AuNPs, and the addition of NaCl induces the aggregation of the unprotected AuNPs, resulting in a decrease in absorbance at the LSPR band (A₅₂₁) and an increase in absorbance at 750 nm (A₇₅₀). The concentration of NT-proBNP showed a linear correlation with the aggregation ratio (A₅₂₁/A₇₅₀), and the assay demonstrated a limit of detection (LOD) of 0.303 µg·L^-1 and a detection range of 0.566-8 µg·L^-1. However, the presence of sulfur-containing proteins in saliva and fetal bovine serum hindered the detection of NT-proBNP in these biofluids. Nevertheless, the assay successfully detected NT-proBNP in diluted urine with an LOD of 0.417 µg·L^-1 and a detection range of 0.589-6 µg·L^-1. The observed values in urine samples from preterm infants with cardiovascular disease fell within this range, indicating the potential clinical relevance of the assay. The recovery percentages ranged from 92.3 to 116.3%. Overall, our findings suggest that the LSPR-based assay for NT-proBNP detection in urine can be a valuable tool for the diagnosis and treatment of cardiovascular disease.

Progress in the Optical Sensing of Cardiac Biomarkers

Biomarkers play key roles in the diagnosis, risk assessment, treatment and supervision of cardiovascular diseases (CVD). Optical biosensors and assays are valuable analytical tools answering the need for fast and reliable measurements of biomarker levels. This review presents a survey of recent literature with a focus on the past 5 years. The data indicate continuing trends towards multiplexed, simpler, cheaper, faster and innovative sensing while newer tendencies concern minimizing the sample volume or using alternative sampling matrices such as saliva for less invasive assays. Utilizing the enzyme-mimicking activity of nanomaterials gained ground in comparison to their more traditional roles as signaling probes, immobilization supports for biomolecules and for signal amplification. The growing use of aptamers as replacements for antibodies prompted emerging applications of DNA amplification and editing techniques. Optical biosensors and assays were tested with larger sets of clinical samples and compared with the current standard methods. The ambitious goals on the horizon for CVD testing include the discovery and determination of relevant biomarkers with the help of artificial intelligence, more stable specific recognition elements for biomarkers and fast, cheap readers and disposable tests to facilitate rapid testing at home. As the field is progressing at an impressive pace, the opportunities for biosensors in the optical sensing of CVD biomarkers remain significant.

Application of Shear Horizontal Surface Acoustic Wave (SH-SAW) Immunosensor in Point-of-Care Diagnosis

Point-of-care testing (POCT), also known as on-site or near-patient testing, has been exploding in the last 20 years. A favorable POCT device requires minimal sample handling (e.g., finger-prick samples, but plasma for analysis), minimal sample volume (e.g., one drop of blood), and very fast results. Shear horizontal surface acoustic wave (SH-SAW) biosensors have attracted a lot of attention as one of the effective solutions to complete whole blood measurements in less than 3 min, while providing a low-cost and small-sized device. This review provides an overview of the SH-SAW biosensor system that has been successfully commercialized for medical use. Three unique features of the system are a disposable test cartridge with an SH-SAW sensor chip, a mass-produced bio-coating, and a palm-sized reader. This paper first discusses the characteristics and performance of the SH-SAW sensor system. Subsequently, the method of cross-linking biomaterials and the analysis of SH-SAW real-time signals are investigated, and the detection range and detection limit are presented.

Aptamer-based sample purification for mass spectrometric quantification of trastuzumab in human serum

In this study, we developed a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay to quantify trastuzumab in human serum using aptamers for sample purification. Trastuzumab was extracted from serum samples using the capture probe based on its aptamer CH1S-3, followed by reduction, alkylation, trypsin digestion, and quantification using LC-MS/MS. Additionally, a unique peptide, FTISADTSK, was employed as a surrogate peptide and quantified, and *FTISADTSK (¹³C₉¹⁵N-labeled phenylalanine) was used as an internal standard to minimize variability in detection among the samples. The detection range for this method was 0.5-250 μg/mL, with a high correlation coefficient (r² > 0.99). The intra- and inter-day precision (%CV, the coefficient of variation) of the quality control samples was less than 12.7%, and the accuracy (%bias) was below 8.64%. After optimization and verification, this assay was used to determine trastuzumab levels in clinical human serum samples. The results indicated that the trastuzumab concentrations had an approximate 4-fold difference among ten patients (range: 11.80-41.90 μg/mL). This study provides a novel approach for the accurate and quantitative monitoring of the mAb-trastuzumab.

Highly sensitive and label-free electrochemical detection of C-reactive protein on a peptide receptor-gold nanoparticle-black phosphorous nanocomposite modified electrode

C-reactive protein (CRP) is a phylogenetically highly conserved plasma protein found in blood serum, and an enhanced CRP level is indicative of inflammatory conditions such as infection and cancer, among others. In this work, we developed a novel high CRP-affinity peptide-functionalized label-free electrochemical biosensor for the highly sensitive and selective detection of CRP. Throughout biopanning with random peptide libraries, high affinity peptides for CRP was successfully identified, and then a series of synthetic peptide receptor, of which C-terminus was incorporated to gold binding peptide (GBP) as an anchoring motif was covalently immobilized onto gold nanoparticle (AuNPs) tethered polydopamine (PDA)‒black phosphorus (BP) (AuNPs@BP@PDA) nanocomposite electrode. Interaction between the CRP-binding peptide and CRP was confirmed via enzyme-linked immunosorbent assay along with various physicochemical and electrochemical analyses. Under the optimized experimental conditions, the proposed peptide-based biosensor detects CRP in the range of 0-0.036 μg/mL with a detection limit (LOD) of 0.7 ng/mL. The developed sensor effectively detects CRP in the real samples of serum and plasma of Crohn's disease patients. Thus, the fabricated peptide-based biosensor has potential applications in clinical diagnosis and medical applications.

A dual-mode sensor based on colorimetric and Tyndall effect of gold nanoparticles for ultra-sensitive detection of Hg2

Mercury ion (Hg²⁺) is the most widespread and highly toxic environmental pollutant, which exerts numerous adverse effects on environmental and human health. There is an urgent need to develop a convenient method for detecting Hg²⁺. Herein, a novel dual-mode sensor based on colorimetric and Tyndall effect of gold nanoparticles was developed for ultra-sensitive determination of Hg²⁺. In this strategy, a polyA-modified Au probe with high uniformity was assembled successfully. Both modes were based on Hg²⁺-induced aggregation of the probes. Hg²⁺ was reflected according to the color variations of solution and the Tyndall effect of Au reporter. With the aid of a laser pointer, the Tyndall mode demonstrated about 615-fold improvement on sensitivity compared with the colorimetry way. Taking advantages of low cost and convenient assembly of polyA-based Au probe and the combination of colorimetry and Tyndall effect, our strategy determined the Hg²⁺ with high sensitivity and wide range. By changing probes or nanoparticles, the proposed strategy is expected to be a universal platform for detecting other analytes in environmental and even biological samples. A novel dual-mode sensor based on colorimetric and tyndall effect of gold nanoparticles for ultra-sensitive determination of Hg2+ was exploited.

Interaction of Colloidal Gold Nanoparticles with Urine and Saliva Biofluids: An Exploratory Study

The use of gold nanoparticles for drug delivery, photothermal or photodynamic therapy, and biosensing enhances the demand for knowledge about the protein corona formed on the surface of nanoparticles. In this study, gold nanospheres (AuNSs), gold nanorods (AuNRs), and gold nanoflowers (AuNFs) were incubated with saliva or urine. After the interaction, the surface of gold nanoparticles was investigated using UV-VIS spectroscopy, zeta potential, and dynamic light scattering. The shifting of the localized surface plasmon resonance (LSPR) band, the increase in hydrodynamic diameter, and the changes in the surface charge of nanoparticles indicated the presence of biomolecules on the surface of AuNSs, AuNRs, and AuNFs. The incubation of AuNFs with saliva led to nanoparticle aggregation and minimal protein adsorption. AuNSs and AuNRs incubated in saliva were analyzed through liquid chromatography with tandem mass spectrometry (LC-MS/MS) to identify the 96 proteins adsorbed on the surface of the gold nanoparticles. Among the 20 most abundant proteins identified, 14 proteins were common in both AuNSs and AuNRs. We hypothesize that the adsorption of these proteins was due to their high sulfur content, allowing for their interaction with gold nanoparticles via the Au-S bond. The presence of distinct proteins on the surface of AuNSs or AuNRs was also investigated and possibly related to the competition between proteins present on the external layers of corona and gold nanoparticle morphology.

A facile aptamer-based sensing strategy for dopamine detection through the fluorescence energy transfer between dye and single-wall carbon nanohorns

Dopamine (DBA) as an important biomarker, plays a crucial role in disease diagnosis. In this study, we have developed a fast and simple aptamer-based fluorescence strategy which used single-wall carbon nanohorns (SWCNHs) as a quencher for dopamine detection. SWCNHs were negatively charged after pretreated, which improved its dispersion in solution. 5-carboxy-fluorescein (FAM) was used to label dopamine aptamer. In the absence of dopamine, FAM-modified aptamer could be absorbed onto the SWCNHs surface due to π-π interaction, resulting in the fluorescence intensity decreased. Dopamine could specifically bind with FAM-DNA to form G-quadruplex, which could not be absorbed onto the surface of SWCNHs. Hence, the fluorescence of FAM-DNA recovered, and the fluorescent intensity as a function of different concentrations of dopamine was measured. We obtained a detection limit of 5 μM for this detection system with a linear detection range of 0.02-2.20 mM. Furthermore, the feasibility of the innovative detection system has been verified by detecting dopamine in spiked serum samples.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Aptamer-Based Biosensors for the Colorimetric Detection of Blood Biomarkers: Paving the Way to Clinical Laboratory Testing

Clinical diagnostics for human diseases rely largely on enzyme immunoassays for the detection of blood biomarkers. Nevertheless, antibody-based test systems have a number of shortcomings that have stimulated a search for alternative diagnostic assays. Oligonucleotide aptamers are now considered as promising molecular recognizing elements for biosensors (aptasensors) due to their high affinity and specificity of target binding. At the moment, a huge variety of aptasensors have been engineered for the detection of various analytes, especially disease biomarkers. However, despite their great potential and excellent characteristics in model systems, only a few of these aptamer-based assays have been translated into practice as diagnostic kits. Here, we will review the current progress in the engineering of aptamer-based colorimetric assays as the most suitable format for clinical lab diagnostics. In particular, we will focus on aptasensors for the detection of blood biomarkers of cardiovascular, malignant, and neurodegenerative diseases along with common inflammation biomarkers. We will also analyze the main obstacles that have to be overcome before aptamer test systems can become tantamount to ELISA for clinical diagnosis purposes.

A rapid fluorescent aptasensor for point-of-care detection of C-reactive protein

In this paper, we report on a novel fluorescent aptasensor based on aptamers modified by both nitrogen-doped graphene quantum dots (N-GQDs) and gold nanoparticles (AuNPs) for the detection of C-reactive protein (CRP). FRET effect is utilized in our aptasensor by the change of aptamers conformation when binding with the target. An obvious fluorescence quench of the N-GQDs can be observed when CRP appears in the assay due to electron transfer between the donor and accepter. A detection limit of 0.2 ng/mL can be achieved by our sensor in PBS buffer which is much lower than the physiological CRP level in human serum. Also, CRP levels in different patients' serum are tested with our assay. Since our aptasensor is rapid (detection time less than 40 min), one-step and very simple to operate, we believe it has great potential to apply for point-of-care testing (POCT).

Aptamers Targeting Cardiac Biomarkers as an Analytical Tool for the Diagnostics of Cardiovascular Diseases: A Review

The detection of cardiac biomarkers is used for diagnostics, prognostics, and the risk assessment of cardiovascular diseases. The analysis of cardiac biomarkers is routinely performed with high-sensitivity immunological assays. Aptamers offer an attractive alternative to antibodies for analytical applications but, to date, are not widely practically implemented in diagnostics and medicinal research. This review summarizes the information on the most common cardiac biomarkers and the current state of aptamer research regarding these biomarkers. Aptamers as an analytical tool are well established for troponin I, troponin T, myoglobin, and C-reactive protein. For the rest of the considered cardiac biomarkers, the isolation of novel aptamers or more detailed characterization of the known aptamers are required. More attention should be addressed to the development of dual-aptamer sandwich detection assays and to the studies of aptamer sensing in alternative biological fluids. The universalization of aptamer-based biomarker detection platforms and the integration of aptamer-based sensing to clinical studies are demanded for the practical implementation of aptamers to routine diagnostics. Nevertheless, the wide usage of aptamers for the diagnostics of cardiovascular diseases is promising for the future, with respect to both point-of-care and laboratory testing.

Recent advances in aptamer applications for analytical biochemistry

Aptamers are typically defined as relatively short (20-60 nucleotides) single-stranded DNA or RNA molecules that bind with high affinity and specificity to various types of targets. Aptamers are frequently referred to as "synthetic antibodies" but are easier to obtain, less expensive to produce, and in several ways more versatile than antibodies. The beginnings of aptamers date back to 1990, and since then there has been a continual increase in aptamer publications. The intent of the present account was to focus on recent original research publications, i.e., those appearing in 2019 through April 2020, when this account was written. A Google Scholar search of this recent literature was performed for relevance-ranking of articles. New methods for selection of aptamers were not included. Nine categories of applications were organized and representative examples of each are given. Finally, an outlook is offered focusing on "faster, better, cheaper" application performance factors as key drivers for future innovations in aptamer applications.

The effect of layer thickness and immobilization chemistry on the detection of CRP in LSPR assays

The immobilization of a capture molecule represents a crucial step for effective usage of gold nanoparticles in localized surface plasmon resonance (LSPR)-based bioanalytics. Depending on the immobilization method used, the resulting capture layer is of varying thickness. Thus, the target binding event takes place at different distances to the gold surface. Using the example of a C-reactive protein immunoassay, different immobilization methods were tested and investigated with regard to their resulting target signal strength. The dependency of the target signal on the distance to the gold surface was investigated utilizing polyelectrolyte bilayers of different thickness. It could be experimentally demonstrated how much the LSPR-shift triggered by a binding event on the gold nanoparticles decreases with increasing distance to the gold surface. Thus, the sensitivity of an LSPR assay is influenced by the choice of immobilization chemistry.

Biophysical Characterization of Novel DNA Aptamers against K103N/Y181C Double Mutant HIV-1 Reverse Transcriptase

The human immunodeficiency virus type-1 Reverse Transcriptase (HIV-1 RT) plays a pivotal role in essential viral replication and is the main target for antiviral therapy. The anti-HIV-1 RT drugs address resistance-associated mutations. This research focused on isolating the potential specific DNA aptamers against K103N/Y181C double mutant HIV-1 RT. Five DNA aptamers showed low IC50 values against both the KY-mutant HIV-1 RT and wildtype (WT) HIV-1 RT. The kinetic binding affinity forms surface plasmon resonance of both KY-mutant and WT HIV-1 RTs in the range of 0.06–2 μM and 0.15–2 μM, respectively. Among these aptamers, the KY44 aptamer was chosen to study the interaction of HIV-1 RTs-DNA aptamer complex by NMR experiments. The NMR results indicate that the aptamer could interact with both WT and KY-mutant HIV-1 RT at the NNRTI drug binding pocket by inducing a chemical shift at methionine residues. Furthermore, KY44 could inhibit pseudo-HIV particle infection in HEK293 cells with nearly 80% inhibition and showed low cytotoxicity on HEK293 cells. These together indicated that the KY44 aptamer could be a potential inhibitor of both WT and KY-mutant HIV-RT.

A robust colorimetric aptasensor for the label-free detection of marine toxins based on tyrosine-capped gold nanoparticles

Tyrosine-capped AuNPs decrease the interaction between targets and AuNPs, presenting better robustness than traditional Cit-AuNPs. Utilizing the superior features, a label-free aptasensor is developed for marine toxin detection for the first time.

Nanomaterial-based aptasensors as an efficient substitute for cardiovascular disease diagnosis: Future of smart biosensors

As a major cause of deaths in developed countries, cardiovascular disease (CVD) has been a big burden for human health systems. Its early and rapid detection is crucial to efficiently apply appropriate on time therapy and to ultimately reduce the associated mortality rate. Aptamers, known as single-stranded DNA/RNA or oligonucleotides containing receptors and/or catalytic properties, have been widely employed in biodetection platforms due to their beneficial properties. Like antibodies, aptamers have served as artificial target receptors in affinity biosensors. Currently, advanced biosensors with improved sensitivity and specificity are fabricated by the synergistic combination of aptamers and diverse nanomaterials. Herein, we review the current development and applications of nanomaterial-based aptasensors for the recognition of CVD biomarkers with special emphasis on electrochemical and optical technologies. The performance of aptasensors has been assessed further in terms of key quality assurance metrics along with discussions on recent technologies developed for the amplification of signals with enhanced portability.

Nanoparticle-based colorimetric sensors to detect neurodegenerative disease biomarkers

Neurodegenerative disorders (NDDs) are progressive, incurable health conditions that primarily affect brain cells, and result in loss of brain mass and impaired function. Current sensing technologies for NDD detection are limited by high cost, long sample preparation, and/or require skilled personnel. To overcome these limitations, optical sensors, specifically colorimetric sensors, have garnered increasing attention towards the development of a cost-effective, simple, and rapid alternative approach. In this review, we evaluate colorimetric sensing strategies of NDD biomarkers (e.g. proteins, neurotransmitters, bio-thiols, and sulfide), address the limitations and challenges of optical sensor technologies, and provide our outlook on the future of this field.

Advances in Colorimetric Assay Based on AuNPs Modified by Proteins and Nucleic Acid Aptamers

This review is focused on the biosensing assay based on AuNPs (AuNPs) modified by proteins, peptides and nucleic acid aptamers. The unique physical properties of AuNPs allow their modification by proteins, peptides or nucleic acid aptamers by chemisorption as well as other methods including physical adsorption and covalent immobilization using carbodiimide chemistry or based on strong binding of biotinylated receptors on neutravidin, streptavidin or avidin. The methods of AuNPs preparation, their chemical modification and application in several biosensing assays are presented with focus on application of nucleic acid aptamers for colorimetry assay for determination of antibiotics and bacteria in food samples.

Advances in aptamer-based sensing assays for C-reactive protein

C-reactive protein (CRP), a non-specific acute-phase indicator of inflammation, has been widely recognized for its value in clinical diagnostic applications. With the advancement of testing technologies, there have been many reports on fast, simple, and reliable methods for CRP testing. Among these, the aptamer-based biosensors are the focus and hotspot of research for achieving high-sensitivity analysis of CRP. This review summarizes the progress of in vitro aptamer screening for CRP and the recent advances in aptamer-based CRP sensor applications, thus developing insight for the new CRP aptasensor design strategy.

Fabrication of a surface-enhanced Raman spectroscopy-based analytical method consisting of multifunctional DNA three-way junction-conjugated porous gold nanoparticles and Au-Te nanoworm for C-reactive protein detection

C-Reactive protein (CRP) is a biomarker of inflammatory responses and an index for assessing the risk of cardiovascular disease and estimating prognosis. In this study, we constructed a surface-enhanced Raman spectroscopy (SERS) biosensor composed of a multifunctional DNA three-way junction (DNA 3WJ), porous gold nanoplates (pAuNPs), and an Au-Te nanoworm structure for detection of CRP. The pAuNP and Au-Te nanostructures were synthesized by galvanic replacement reactions, and the morphology was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering (DLS). To generate the SERS signal, the Au-Te nanostructure was immobilized on an indium-tin oxide substrate, and the thiol-modified CRP aptamer was then self-assembled onto the modified substrate for CRP recognition. To amplify the SERS signal and identify the Raman tag, the multifunctional DNA 3WJ was conjugated with the pAuNPs, and each fragment of 3WJ was functionalized to biotin (pAuNP conjugation), methylene blue (Raman reporter), and CRP aptamer (target binding). The results were confirmed by gel electrophoresis. For conjugation between pAuNPs and DNA 3WJ, avidin was encapsulated in pAuNPs, and the conjugation structure was confirmed by DLS. The fabricated SERS biosensor showed detection limits of 2.23 pM in phosphate-buffered saline and 3.11 pM in diluted human serum. Overall, the proposed biosensor may have potential applications as a SERS biosensor platform.

Visual detection of tropomyosin, a major shrimp allergenic protein using gold nanoparticles (AuNPs)-assisted colorimetric aptasensor

A gold nanoparticle-based label-free colorimetric assay was developed to detect the shrimp allergenic protein tropomyosin (TM), an important biomarker responsible for severe clinical reactivity to shellfish. In a gold nanoparticles (AuNPs)-tropomyosin-binding aptamer (TMBA) complex, the aptamer adsorbs onto the surface of AuNPs and dissociates in the presence of TM. In addition, AuNPs tend to aggregate in the presence of ionic salt, revealing a color change (i.e., wine-red to purple/blue) with a shift in the maximum absorption peak from 520 nm. In the presence of specific binding TM, the aptamer folds into a tertiary structure where it more efficiently stabilizes AuNPs toward the salt-induced aggregation with a hypsochromic shift in the absorption spectra compared to the stabilized AuNPs by aptamer alone. Based on the aggregation and sensitive spectral transformation principle, the AuNPs-based colorimetric aptasensor was successfully applied to detect TM with a range of 10-200 nmol/L and a low detection limit of 40 nmol/L in water samples. The reliability, selectivity, and sensitivity of the aptasensor was then tested with food samples spiked with TM. The observed detection limit was as low as 70 nmol/L in shrimp, 90 nmol/L in tofu, and 80 nmol/L in eggs, respectively. We anticipate the proposed AuNPs-based colorimetric aptasensor assay possesses a high potential for the easy and efficient visual colorimetric detection of TM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-020-00085-5.

Fabrication of a sensitive colorimetric nanosensor for determination of cysteine in human serum and urine samples based on magnetic-sulfur, nitrogen graphene quantum dots as a selective platform and Au nanoparticles

A novel colorimetric nanosensor is reported for the selective and sensitive determination of cysteine using magnetic-sulfur, nitrogen graphene quantum dots (Fe₃O₄/S, N-GQDs), and gold nanoparticles (Au NPs). Thus, S, N-GQDs was firstly immobilized on Fe₃O₄ nanoparticles through its magnetization in the presence of Fe³⁺ in the alkali solution. The prepared Fe₃O₄/S, N-GQDs were dispersed in cysteine solution resulting in its quick adsorption on the surface of the Fe₃O₄/S, N-GQDs through hydrogen bonding interaction. Then, Au NPs solution was added to this mixture that after a short time, the color of Au NPs changed from red to blue, the intensity of surface plasmon resonance peak of Au NPs at 530 nm decreased, and a new peak at a higher wavelength of 680 nm appeared. The effective parameters on cysteine quantification were optimized via response surface methodology using the central composite design. Under optimum conditions, the absorbance ratio (A₆₈₀/A₅₃₀) has a linear proportionality with cysteine concentration in the range of 0.04-1.20 μmol L^-1 with a limit of detection of 0.009 μmol L^-1. The fabrication of the reported nanosensor is simple, fast, and is capable of efficient quantification of ultra traces of cysteine in human serum and urine real samples.

Numerical Modelling of the Optical Properties of Plasmonic and Latex Nanoparticles to Improve the Detection Limit of Immuno-Turbidimetric Assays

Turbidimetric assays with latex nanoparticles are widely applied for the detection of biological analytes, because of their rapidity, low cost, reproducibility, and automatization. However, the detection limit can be lowered only at the price of a reduced dynamic range, due to the rapid saturation of the light scattering signal at high analyte concentration. Here, we use numerical calculations to investigate the possibility of increasing the performance of immuno-turbidimetric assays without compromising the measurement dynamic range, by combining plasmonic (gold, silver) and latex nanoparticles. Our modelling results show that plasmonic nanoparticles are compatible with a large signal change even when small aggregates are formed, i.e., at low analyte concentration. The working principle relies on the remarkable modification of the surface plasmon band when noble metal nanoparticles form oligomers, and also when latex particles are included in the aggregate. At high analyte concentration, when larger aggregates form, the latex particles can provide the required linear response of standard immuno-turbidimetric assays. Thus, the combination of the two components can be a successful strategy to improve the detection limit and the dynamic range, while maintaining all the advantages of the homogeneous immuno-turbidimetric assays.

Recent Advances in CRP Biosensor Based on Electrical, Electrochemical and Optical Methods

C-reactive protein (CRP) is an acute-phase reactive protein that appears in the bloodstream in response to inflammatory cytokines such as interleukin-6 produced by adipocytes and macrophages during the acute phase of the inflammatory/infectious process. CRP measurement is widely used as a representative acute and chronic inflammatory disease marker. With the development of diagnostic techniques measuring CRP more precisely than before, CRP is being used not only as a traditional biomarker but also as a biomarker for various diseases. The existing commercialized CRP assays are dominated by enzyme-linked immunosorbent assay (ELISA). ELISA has high selectivity and sensitivity, but its limitations include requiring complex analytic processes, long analysis times, and professional manpower. To overcome these problems, nanobiotechnology is able to provide alternative diagnostic tools. By introducing the nanobio hybrid material to the CRP biosensors, CRP can be measured more quickly and accurately, and highly sensitive biosensors can be used as portable devices. In this review, we discuss the recent advancements in electrochemical, electricity, and spectroscopy-based CRP biosensors composed of biomaterial and nanomaterial hybrids.

Gold nanoparticles-based assays for biodetection in urine

Urine is a biofluid easy to collect through a non-invasive technique that allows collecting a large volume of sample. The use of urine for disease diagnosis is not yet well explored. However, it has gained attention over the last three years. It has been applied in the diagnosis of several illnesses such as kidney disease, bladder cancer, prostate cancer and cardiovascular diseases. In the last decade, gold nanoparticles (Au NPs) have attracted attention in biosensors' development for the diagnosis of diseases due to their electrical and optical properties, ability to conjugate with biomolecules, high sensitivity, and selectivity. Therefore, this article aims to present a comprehensive view of state of the art on the advances made in the quantification of analytes in urinary samples using AuNPs based assays, with a focus on protein analysis. The type of diagnosis methods, the Au NPs synthesis approaches and the strategies for surface modification aiming at selectivity towards the different targets are highlighted.

An apta-aggregation based machine learning assay for rapid quantification of lysozyme through texture parameters

A novel assay technique that involves quantification of lysozyme (Lys) through machine learning is put forward here. This article reports the tendency of the well- documented Ellington group anti-Lys aptamer, to produce aggregates when exposed to Lys. This property of apta-aggregation has been exploited here to develop an assay that quantifies the Lys using texture and area parameters from a photograph of the elliptical aggregate mass through machine learning. Two assay sets were made for the experimental procedure: one with high Lys concentration between 25–100 mM and another with low concentration between 1–20 mM. The high concentration set had a sample volume of 10 μl while the low concentration set had a higher sample volume of 100 μl, in order to obtain the statistical texture values reliably from the aggregate mass. The platform exhibited an experimental limit of detection of 1 mM and a response time of less than 10 seconds. Further, two potential operating modes for the aptamer were hypothesized for this aggregation property and the more accurate mode among the two was ascertained through bioinformatics studies.

Functionalized ultra-fine bimetallic PtRu alloy nanoparticle with high peroxidase-mimicking activity for rapid and sensitive colorimetric quantification of C-reactive protein

The in situ synthesis is reported of citric acid-functionalized ultra-fine bimetallic PtRu alloy nanoparticles (CA@PtRu ANPs) through a simple one-pot wet chemical method. The cost-efficient CA@PtRu ANPs with an average diameter of 3.2 nm revealed to have enhanced surface area, peroxidase-like activity, high stability, and adequate availability of functional groups to bind biomolecules. Along with nanoparticle surface area, the surface charge has also significantly affected the peroxidase-like activity and the colloidal suspension stability. As an excellent immobilization matrix and peroxidase mimic, the CA@PtRu ANPs were utilized to develop non-enzymatic colorimetric immunoassay for rapid, selective, and sensitive quantification of C-reactive protein (CRP) biomarkers. In this immunoassay, CA@PtRu ANPs serve as enzyme mimic that significantly amplifies the color signals, and amine-functionalized silica-coated magnetic microbeads (APTES/SiO₂@Fe₃O₄) act as CRP-recognizing capture probes. The absorbance curves of colorimetric immunoassay were measured in wavelengths between 550 and 750 nm, and the maximum absorbance at 652 nm was used to establish a linear relationship between absorbance and CRP concentrations. The developed colorimetric immunoassay showed rapid and sensitive quantification of CRP levels from 0.01 to 180 μg mL^-1 with a LOD of 0.01 μg mL^-1. Moreover, the mean recovery of CRP from spiked human serum samples lies between 97 and 109% (n = 3), which indicates that the proposed nanozyme-linked immunoassay has the potential to be used in rapid point-of-care applications.

Rapid and sensitive detection of melanin using glutathione conjugated gold nanocluster based fluorescence quenching assay

In the present study, a rapid, facile, and highly sensitive assay based on glutathione conjugated gold nanocluster (GSH-AuNCs) is developed for the detection of melanin. The analysis of melanin which is linked to several diseases is crucial. The current methods for melanin estimation are complex and long, thus demands an alternative technology. In general, melanin exhibits photoactive properties, thus, it might have fluorescence quenching properties through the phenomenon of fluorescence resonance energy transfer. To verify our assumption, we have developed the fluorescence quenching assay based on gold nanocluster and melanin interaction. As a result, under the optimized condition, the developed quenching assay demonstrated the high selectivity and sensitivity toward melanin with a limit of detection and correlation coefficient of 0.060 μg/mL and 0.993, respectively. Moreover, the whole process represented the rapid assay time of 30 min to complete. To validate the performance of our assay on real samples, B16F1 cells lysate, and hair samples were tested that provided satisfactory results. Therefore, we believe that our assay due to good sensitivity and short assay time could be beneficial for the clinical diagnosis of melanin in the future study.

An electrochemical immunosensor coupling a bamboo-like carbon nanostructure substrate with toluidine blue-functionalized Cu(ii)-MOFs as signal probes for a C-reactive protein assay

In this paper, a novel sandwich immunosensor based on a toluidine blue (Tb) loaded metal organic framework (Cu(ii)-HKUST-1/Tb) as the signal element and a nitrogen-doped 3D carbon nanostructure as the electrode substrate was constructed for the detection of C-reactive protein (CRP). Tb as an electrochemically active agent usually forms a polymer by aggregation in the solvent, causing a poor electrochemical response. Therefore, in order to overcome this obstacle, Cu(ii)-HKUST-1 with a porous nanostructure and large specific surface area as a carrier could adsorb a large number of Tb molecules on its surface to improve its electrochemical performance. In addition, the high electron transfer efficiency of the N-doped bamboo-like carbon nanotubes (CoFe/N-GCT) improves the sensitivity of the biosensor. Differential pulse voltammetry (DPV) was used to detect the current signal of Tb at -0.2 V. The current response increased with the increase in concentration of CRP, ranging from 0.5 to 200 ng mL-1. The detection limit is 166.7 pg mL-1 (S/N = 3). Moreover, the proposed biosensor can be applied in real serum sample detection. It has potential applications in the field of biomedicine assays.

Colorimetric recognition of aromatic amino acid enantiomers by gluconic acid-capped gold nanoparticles

In this work, we prepared gold nanoparticles (AuNPs) by employing gluconic acid (GlcA) as reducing-cum-stabilizing agent. The proposed GlcA-AuNPs successfully worked as a colorimetric sensor for visual chiral recognition of aromatic amino acid enantiomers, namely tyrosine (D/L-Tyr), phenylalanine (D/L-Phe), and tryptophan (D/L-Trp). After adding L-types to GlcA-AuNPs solution, the color of the mixture changed from red to purple (or gray), while no obvious color change occurred on the addition of D-types. The effect can be detected by naked eyes. The particles have been characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, zeta potential, the dynamic light scattering analysis as well as UV-Vis spectroscopy. This assay can be used to determine the enantiomeric excess of L-Trp in the range from 0 to + 100%. The method has advantages in simplicity, sensitivity, fast response, and low cost.

Handheld pH meter-assisted immunoassay for C-reactive protein using glucose oxidase-conjugated dendrimer loaded with platinum nanozymes

A simple and feasible pH meter-based immunoassay is reported for detection of C-reactive protein (CRP) using glucose oxidase (GOD)-conjugated dendrimer loaded with platinum nanozyme. Initially, platinum nanozymes were loaded into the dendrimers through an in situ synthetic method. Then, GOD and monoclonal anti-CRP antibody with a high molar ratio were covalently conjugated onto carboxylated dendrimers via typical carbodiimide coupling. The immunoreaction was carried out with a competitive mode in a CRP-coated microplate. Along with formation of immunocomplex, the added glucose was oxidized into gluconic acid and hydrogen peroxide by GOD, and the latter was further decomposed by platinum nanozyme, thus accelerating chemical reaction in the positive direction. The produced gluconic acid changed the pH of detection solution, which was determined using a handheld pH meter. Under optimum conditions, the pH meter-based immunoassay gave a good signal toward target CRP from 0.01 to 100 ng mL-1. The limit of detection was 5.9 pg mL-1. An intermediate precision ≤ 11.2% was acquired with batch-to-batch identification. No nonspecific adsorption was observed during a series of procedures to detect target CRP, and the cross-reaction against other biomarkers was very low. Importantly, our system gave well-matched results for analysis of human serum samples relative to a referenced ELISA kit.Graphical abstract.