Electroactive Label Research Articles

Electroactive RuPt NPs programmed dual-channel electrochemical sensor for methyl mercaptan monitoring

The accurate and sensitive detection of methyl mercaptan (CH3SH) was of great significance for food corruption monitoring. Electroactive labels engineered electrochemical sensors possessed tailorable electrochemical responses, and showed potential prospects for CH3SH monitoring. In comparison to a single electrochemical signal, electroactive nanocomposites with multiple electrochemical responses not only provided multi-channel sensing signals for accurate detection, but also increased the peak intensity for sensitive detection. Herein, RuPt NPs were designed and explored to possess two independent and non-interfering electrochemical oxidation peaks at 0.75 V and −0.73 V. The formation of metal-SH covalent bonds between electroactive sites of RuPt NPs and CH3SH induced the changes of two electrochemical oxidation peaks. By utilizing the sum intensity of two electrochemical peaks as detection signal, a dual-channel electrochemical sensor was established for CH3SH detection in the range of 1 μM-1 mM, and had a low limit of detection (LOD) of 300 nM. This work gave a new insight into promoting more electroactive nanocomposites with multiple signals for accurate and sensitive electrochemical detection applications.

A review of antibody, aptamer, and nanomaterials synergistic systems for an amplified electrochemical signal.

The synergy between biomolecules with inorganic nanomaterials and nanoparticles has been investigated over the past years, primarily to improve biomarker reception, generate signals, and amplify the signals generated. In this paper, several articles on aptamer-based and antibody-based electrochemical biosensors that target antigens were examined. Among the key characteristics identified were the electrochemical platform development, which includes the usage of nanomaterials as electroactive or electrocatalytic labels, crosslinking of the biological agent with inorganic compounds, and electrode coating to provide an electronic source and support efficient electron transfer. A single approach using labeled or unlabeled biological receptors has become advantageous due to its simple architecture and more straightforward application method. However, the dual system approach allows the incorporation of more nanomaterials to boost the signal and add more features to the electrochemical system. The dual system approach uses a capture and reporter probe in a competitive or sandwich detection format. The reporter probe is often labeled by an electroactive or electrocatalytic compound or immobilized in a nanocarrier, resulting in an increase in measured peak current in proportion to the target's concentration. The reported limit of detection and linear range for each platform is presented to assess its efficiency. Generally, the dual system aptasensor showed higher sensitivity, stability, and reproducibility than the immunosensor in comparable settings. The aptasensor showed promising results for the development of point-of-care type applications.

Polymerase incorporation of 4-nitrophenyl modified 2′-deoxyuridine-5′-triphosphates into double-stranded DNA for direct electrochemical detection

Three novel 2′-deoxyuridine-5′-triphosphates modified with 4-nitrophenyl groups via various linkers (dUTP-N1, dUTP-N2, and dUTP-N3) were tested as bearers of reducible electroactive labels as well as substrates suitable for enzymes used in polymerase chain reaction (PCR) and recombinase polymerase amplification (RPA) with a potential application to direct electrochemical detection of double-stranded deoxyribonucleic acid (dsDNA). In cyclic and square wave voltammograms on carbon screen printed electrodes, the labeled dUTP have demonstrated distinct reduction peaks at potentials of –0.7 V to –0.9 V (phosphate buffer, pH 7.4). The reduction peak currents of dUTP-N derivatives were found to increase with their molar concentrations. The dUTP-N3 with a double bond in the linker had the lowest reduction potential (about 100 mV less negative) among the derivatives studied. Further, dUTP-N nucleotides were tested as substrates in PCR and RPA to incorporate the electroactive labels into 90, 210, or 206 base pair long dsDNA amplicons. However, only a dUTP-N1 derivative with a shorter linker without the double bond demonstrated satisfactory compatibility with both PCR and RPA, though with a low reaction output of modified dsDNA amplicons (at 100% substitution of dTTP). The dsDNA amplicons produced by PCR with 85% substitution of dTTP by the dUTP-N1 in the reaction mixture were successfully detected by square wave voltammetry at micromolar concentrations at high square wave frequency.

Ultrasensitive Detection of Hydrogen Peroxide Using Methylene Blue Grafted on Molecular Wires as Nanozyme with Catalase-like Activity.

In this study, we present the development of an electrochemical sensor designed for ultrasensitive detection of endogenous H2O2. This sensor relies on signal amplification achieved through nanozyme activity exhibited by methylene blue (MB) grafted onto a peptide support. The sensor exhibited excellent selectivity and sensitivity, with a limit of detection of 18 nM and a linear detection range of 20-200 nM. Thus, we have validated the concept of the MB-peptide system, serving as both an electroactive label and a catalyst for H2O2 decomposition under electrochemical conditions. The implemented signal amplification system enables the rapid detection of H2O2, with an overall assay time of 1-2 min, a significant improvement compared to amperometric detection using surface-immobilized enzymes.

Polymerase incorporation of fluorescein or rhodamine modified 2′-deoxyuridine-5′-triphosphates into double-stranded DNA for direct electrochemical detection

The 2′-deoxyuridine-5′-triphosphates modified with fluorescein (dUTP-Fl) or rhodamine (dUTP-Rh) were tested as bearers of electroactive labels and as proper substrates for polymerases used in polymerase chain reaction (PCR) and isothermal recombinase polymerase amplification (RPA) with the aim of electrochemical detection of double-stranded DNA (dsDNA) amplification products. For this purpose, electrochemical behavior of free fluorescein and rhodamine as well as the modified nucleotides, dUTP-Fl and dUTP-Rh, was studied by cyclic (CV) and square wave (SWV) voltammetry on carbon screen printed electrodes. Both free fluorescein and dUTP-Fl underwent a two-step oxidation at the peak potentials (Ep) of 0.6–0.7 V and 0.8–0.9 V (phosphate buffer, pH 7.4). The reduction peaks of fluorescein and dUTP-Fl were registered between –0.9 V and −1 V, but they did not depend on concentration. The free rhodamine and dUTP-Rh have demonstrated the well-defined oxidation peaks at 0.8–0.9 V. In addition, the distinct reduction peaks at Ep between –0.8 V and −0.9 V were registered for both rhodamine and dUTP-Rh. The dUTP-Fl and dUTP-Rh were further tested as substrates to incorporate an electroactive label into 210 or 206 base pair long dsDNA amplicons generated either by PCR or RPA. Among two dUTP derivatives tested, dUTP-Fl revealed significantly better compatibility with PCR and RPA, producing the full-size amplicons at 50–90% substitution of dTTP in the reaction mixture. In the PCR, the best compromise between amplicon output and labeling was achieved at the dUTP-Fl : dTTP and dUTP-Rh : dTTP molar ratios of 70% : 30% and 20% : 80% in the PCR mixture, respectively, allowing the direct electrochemical detection of amplicons at micromolar concentrations. Alongside with fluorescence DNA assays, the fluorescein and rhodamine modified dUTP appear as promising electroactive labels to develop direct electrochemical DNA assays for detecting PCR and RPA products.

Biosensor with electrochemically active nanocomposites for signal amplification and simultaneous detection of three ovarian cancer biomarkers

The current trend in medical diagnostic methods is to simplify and accelerate diagnosis and bring testing closer to the patient while maintaining the existing analytical criteria. Point-of-care tests (POCT) allow improved screening of population and rapid decisions regarding patient care. In case of cancer, this is a very desirable and valuable factor affecting the survival rate. Biosensors exploiting the bioaffinity interaction of target molecules with specific antibodies, combined with screen-printed electrodes as detection units, meet these criteria perfectly. In this study, we present a new sandwich-type magneto-immunosensor with electrochemical signal-generating nanocomposites that was designed for the simultaneous detection and quantification of three biomarkers associated with ovarian cancer, namely human epididymis protein 4 (HE4), alpha-fetoprotein (AFP), and cancer antigen 125 (CA-125). The simultaneous detection was enabled by three different electroactive nanomaterials, namely gold nanoparticles (AuNPs), and CdTe and PbS core-type quantum dots (QDs), which were conjugated with three specific antibodies. Mesoporous silica nanoparticles (SiNPs) were incorporated in nanocomposite for higher loading of electroactive labels, leading to substantial enhancement of electrochemical signal. Square-wave anodic/cathodic stripping voltammetry was used for the detection of metal ions released quantitatively from the captured bioconjugates. Combination of these three elements provided separate non-interfering signals, hence enabling simultaneous detection. Using this multiplex immunosensor, up to three biomarkers within the linear concentration ranges of 0.02–20 pM for HE4, 0.45–450 IU L− 1 for CA-125, and 0.1–500 ng L− 1 for AFP could be detected and quantified. The analytical parameters obtained fit the requirements of early-stage disease detection.

Simultaneous measurement of ochratoxin A and aflatoxin B1 using a duplexed-electrochemical aptasensor based on carbon nanodots decorated with gold nanoparticles and two redox probes hemin@HKUST-1 and ferrocene@HKUST-1

An electrochemical aptasensor was developed for the simultaneous determination of ochratoxin A (OTA) and aflatoxin B1 (AFB1). Two compounds hemin@HKUST-1 and ferrocene@HKUST-1 were synthesized by encapsulating hemin and ferrocene inside the MOF made by copper nodes and trimesic acid, known as HKUST-1 MOF, and then bind to complementary DNA sequences of OTA aptamer (cDNA1) and AFB1 aptamer (cDNA2), respectively. Then, the hemin@HKUST-1/cDNA1 and ferrocene@HKUST-1/cDNA2 bioconjugates were deposited on the glassy carbon electrode (GCE) modified with carbon nanodots decorated with gold nanoparticles (AuNPs-CNDs). In the absence of the two mycotoxins, the current response related to the electroactive labels of hemin and ferrocene in the discussed bioconjugates have been measured at two separate potentials simultaneously by the differential pulse voltammetry technique (DPV). Using the described aptasensor, it is possible to measure both OTA and AFB1 mycotoxins in the linear concentration range of 1.0 × 10−2 to 100.0 ng mL−1. Also, the detection limits of OTA and AFB1 were 4.3 × 10−3 ng mL−1 and 5.2 × 10−3 ng mL−1, respectively. Finally, the ability of the proposed duplex aptasensor for the simultaneous measurement of OTA and AFB1 in a corn flour sample was investigated and completely satisfactory results were achieved.

Biorecognition element-free electrochemical detection of recombinant glycoproteins using metal-organic frameworks as signal tags

Accurate and sensitive determination of recombinant glycoproteins is in great demand for the treatment of anemia-induced chronic kidney disease and the illegal use of doping agents in sports. In this study, an antibody and enzyme-free electrochemical method for the detection of recombinant glycoproteins was proposed via the sequential chemical recognition of hexahistidine (His6) tag and glycan residue on the target protein under the cooperation interaction of nitrilotriacetic acid (NTA)-Ni2+complex and boronic acid, respectively. Specifically, NTA-Ni2+ complex-modified magnetic beads (MBs-NTA-Ni2+) are employed to selectively capture the recombinant glycoprotein through the coordination interaction between His6 tag and NTA-Ni2+ complex. Then, boronic acid-modified Cu-based metal-organic frameworks (Cu-MOFs) were recruited by glycans on the glycoprotein via the formation of reversible boronate ester bonds. MOFs with abundant Cu2+ ions acted as efficient electroactive labels to directly produce amplified electrochemical signals. By using recombinant human erythropoietin as a model analyte, this method showed a wide linear detection range from 0.01 to 50 ng/mL and a low detection limit of 5.3 pg/mL. With the benefits from the simple operation and low cost, the stepwise chemical recognition-based method shows great promise in the determination of recombinant glycoproteins in the fields of biopharmaceutical research, anti-doping analysis and clinical diagnosis.

A sensitive electrochemical genosensor for measuring gastric cancer biomarker, microRNA-106b, based on asparagine polymerization on carbon quantum dots modified electrode

The aim of this work is to develop an electrochemical genosensor to measure microRNA 106b (miR-106b) as a gastric cancer biomarker. To construct the miR-106b genosensor, asparagine (As) was electropolymerized on the surface of carbon quantum dots modified glassy carbon electrode (CQDs/GCE). In the next step, ssDNA was immobilized on the modified electrode surface (As/CQDs/GCE) and then hybridized with miR-106b. Finally, differential pulse voltammograms of the accumulated chlorogenic acid (CGA), as an electroactive label, on the surface of immobilized ssDNA was recorded before (ssDNA/As/CQDs/GCE) and after hybridization with miR-106b (miR-106b/BSA/ssDNA/As/CQDs/GCE). The difference in the peak current of these two voltammograms was used as an analytical signal to measure of miR-106b. Using this genosensor, a linear concentration range from 1.0 fM to 1.0 µM and a detection limit of 0.39 fM were obtained for the measurement of miR-106b. The obtained data indicate that it is possible to recognize miR-106 from a non-complementary and a single-base mismatch sequence using the genosensor. In addition, the measurement of miR-106b in a human serum sample was successfully performed using the genosensor.

Plasmon-enhanced electroreduction activity of Au-AgPd Janus nanoparticles for ochratoxin a detection

Ochratoxin A (OTA) was a dangerous biological toxin, and would easily contaminate food and induced food safety problems. The development of electrochemical aptasensors by designing strong and anti-interfere electroactive labels could improve the sensitivity and accuracy of OTA detection. In this contribution, novel electroactive Au-AgPd Janus NPs were firstly synthesized and exhibited electroreduction signal at −0.4 V, owing to the reduction process of Pd2+. The electroreduction signal was amplified 1.5 times under local surface plasmon resonance (LSPR) excitation, which could improve the sensitivity of OTA detection. Plasmon-enhanced electroreduction principle of Au-AgPd Janus NPs was verified, which endowed electrochemical aptasensor with high accuracy and anti-interference ability for OTA detection. Au-AgPd Janus NPs served as electrochemical beacon achieved sensitive and accurate OTA detection with the limit of detection (LOD) of 0.98 pM. This work opens up new directions for the construction of electroactive heterostructures for the sensitive and accurate biotoxins electroanalytical applications.

An electrochemical immunosensor for the detection of Glypican-3 based on enzymatic ferrocene-tyramine deposition reaction

An ultrasensitive electrochemical immunosensor based on signal amplification of the deposition of the electroactive ferrocene-tyramine (Fc-Tyr) molecule, catalyzed by horseradish peroxidase (HRP), was constructed for the detection of the liver cancer marker Glypican-3 (GPC3). Functional electroactive molecule Fc-Tyr is reported to exhibit both the enzymatic cascade catalytic activity of tyramine signal amplification (TSA) and the excellent redox properties of ferrocene. In terms of design, the low matrix effects inherent in using the magnetic bead platforms, a quasi-homogeneous system, allowed capturing the target protein GPC3 without sample pretreatment, and loading HRP to trigger the TSA, which induced a large amount of Fc-Tyr deposited on the electrode surface layer by layer as a signal probe for the detection of GPC3. The concept of Fc-Tyr as an electroactive label was validated, GPC3 biosensor exhibited high selectivity and sensitivity to GPC3 in the range of 0.1 ng mL−1–1 μg mL−1. Finally, the sensor was used simultaneously with ELISA to assess GPC3 levels in the serum of clinical liver cancer patients, and the results showed consistency, with a recovery of 98.33–105.35% and a relative standard deviation (RSD) of 4.38–8.18%, providing a theoretical basis for achieving portable, rapid and point of care testing (POCT) of tumor markers.

Development of an electrochemical genosensor for quantitative determination of miR-200a based on the current response of ferrocene-functionalized graphene oxide nanosheets

The present study describes the construction of a sensitive electrochemical genosensor for detection of miR-200a using ferrocene-functionalized graphene oxide nanosheets (Fc-GO) as an electroactive label. For this purpose, a glassy carbon electrode (GCE) was modified by amino-functionalized CuO nanoparticles decorated on MnO2 nanorods (NH2-CuONPs-MnO2NRs). The process of the genosensor construction is confirmed by electrochemical impedance spectroscopy (EIS). A sensing mechanism has been proposed based on the π-stacking interaction between Fc-GO nanosheets and the aromatic bases of DNA. The basis of the assay is based on the interaction of the electroactive label of Fc-GO nanosheets with ss-DNA in the absence of the target and its release after hybridization of the ss-DNA with the target, followed by a severe decrease in the current response. Using the genosensor, miR-200a can be measured in the concentration range of 1.0 fM to 0.1 µM and with a detection limit of 0.29 fM using the differential pulse voltammetry method. Depending on the response of the genosensor, a single-base mismatch as well as a non-complementary-one can be detected from the target sequence. Furthermore, the genosensor is capable of measuring miR-200a in a real sample.

A Review of the Construction of the Nanomaterial & Nanocomposite Based Biosensor for Different Applications

Abstract: The heightened attention to food and health safety has prompted researchers to conduct extensive research on biosensors that quickly detect foodborne microbial toxins and pathogens. Biosensors are a blessing due to their simple, cost-effective technique, but there are still some drawbacks with detection time, detection limit, and resilience. Incorporating functionalized nanomaterials into developing biosensors as catalytic tools, immobilization platforms, or optical or electroactive labels has added a new dimension to addressing these challenges. This review paper aims to discuss the construction of different types of nanomaterial-based biosensors in food safety, exosome detection and finally, cancer detection, as well as highlights the advantages of these biosensors over traditional techniques. In addition, a comparative study between the nanomaterial-based biosensors taking into account the linear range and limits of detectionin these mentioned applications was also conducted. Hence, this paper provides key insights into designing and fabricating biosensors utilizing nanomaterials and opens new avenues in disease and food safety research.

A Nonenzymatic DNA Nanomachine for Detection of Biomolecules by DNA Walker Strategy and Radical Polymerization Signal Amplification

AbstractExternal intervention can make quasi‐mechanical movements in enzyme‐free DNA nanomachine, suggesting the promise of developing novel biosensing systems. The superiority of the “signal‐on” strategies inspired researchers to fabricate sensitive and selective biosensors by combining the advantages of chemical amplification methods with DNA nanomachines. Herein, a smart enzyme‐free DNA nanomachine for biomolecule detection has been developed using DNA walker strategy, Click Chemistry, and electrochemically mediated surface‐initiated atom transfer radical polymerization. When the target biomarker is present, DNA walker (DW) could be unleashed which drives walking on the surface of the DNA‐coated Fe3O4/GCE. Then, this DW hybridized with Azide‐labeled DNA probe1 (H1) and subsequently substituted by DNA probe2 (H2) through walking process. Therefore, the loop of H1 was unlocked to form Azide group available at 3’ end. This procedure is repeated so that each released DW can open multiplex H1 strands, resulted in amplification of the signal. After successive walking, “Click reactions” carried out between Azide and 3‐Butynyl‐2‐bromoisobutyrate for initiating the radical polymerization reaction, which brought a great quantity of the electroactive labels on the electrode surface. The number of labels was quantified by square wave voltammetry which was proportional to the target biomarker concentration. In addition, this electroanalytical devicewas applied successfully for direct determination of biomolecules in real serum, and also showed wide dynamic range, excellent detection limit, storage stability and reproducibility. Thus, the proposed biosensor could be effectually utilized in biomedical research and clinical diagnosis.

Electroactive nanocarbon materials as signaling tags for electrochemical PCR

Electrochemical polymerase chain reaction (PCR) represents a valid alternative to the optical-based PCR due to reduced costs of signaling labels, use of simpler instrumentation, and possibility of miniaturization and portability of the systems, which can facilitate decentralized detection. The high intrinsic electroactivity and strong linear relationship between the material concentration and its redox signal suggest a possible use of oxidized nanocarbon materials as electroactive tags for PCR. Herein, we compared three different nanographene oxide materials namely nGO-1, nGO-2 and nGO-3 as signaling tags for the detection of genetically modified organisms (GMO) by electrochemical PCR. The three materials differ in size, chemical composition as well as type and amount of oxygen functionalities verified by extensive characterization with X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) and electrochemical methods. A sense primer sequence belonging to the Cauliflower Mosaic Virus 35S promoter (a common genetic marker for GMO screening) was used to conjugate to the nanocarbon materials by carbodiimide chemistry before PCR amplification with a biotinylated antisense strand. Finally, the amplified electroactive PCR product was detected, where the reduction signal derived from the electrochemically reducible oxygenated functionalities on the nanocarbon material surface was directly correlated to the presence of GMO. Overall, we were able to correlate the different material characteristics with their performance as electroactive labels and identify the nanocarbon material that exhibits the highest potential to be used as innovative electroactive label for PCR in the amplification and detection of the selected target sequence.

Rapid electrochemical detection of COVID-19 genomic sequence with dual-function graphene nanocolloids based biosensor

Discovered in December 2019, the Severe Acute Respiratory Syndrome Coronavirus 2 (aka SARS-CoV-2 or 2019-nCoV) has attracted worldwide attention and concerns due to its high transmissibility and the severe health consequences experienced upon its infection, particularly by elderly people. Over 329 million people have been infected till date and over 5.5 million people could not survive the respiratory illness known as COVID-19 syndrome. Rapid and low-cost detection methods are of utmost importance to monitor the diffusion of the virus and to aid in the global fight against the pandemic.We propose here the use of graphene oxide nanocolloids (GONC) as an electroactive nanocarbon material that can act simultaneously as a transducing platform as well as the electroactive label for the detection of 2019-nCoV genomic sequences. The ability of GONC to provide an intrinsic electrochemical signal arising from the reduction of the electrochemically reducible oxygen functionalities present on its surface, allows GONC to be used as a simple and sensitive biosensing platform. Different intrinsic electroactivity of the material was obtained at each step of the genosensing process, starting from the immobilization of a short-stranded DNA probe and followed by the incubation with different concentrations of the target 2019-nCoV DNA strand. Monitoring such variations enabled the quantification of the target analyte over a wide dynamic range between 10−10 and 10−5 M.All in all, this proof-of-concept system serves as a stepping stone for the development of a rapid, sensitive and selective analytical tool for the detection of 2019-nCoV as well as other similar viral vectors. The use of cost-effective electrochemical detection methods coupled with the vast availability and suitability of carbon-based nanomaterials make this sensing system a valid candidate for low-cost and point-of-care analysis.

Development of an electrochemical aptasensor based on Au nanoparticles decorated on metal-organic framework nanosheets and p-biphenol electroactive label for the measurement of aflatoxin B1 in a rice flour sample.

This study purposes designing a new aptasensor to detect aflatoxin B1 (AFB1). The AFB1 aptasensor was developed by growing gold nanoparticles on the surface of nickel-based metal-organic framework nanosheets (AuNPs/Ni-MOF) and an electroactive indicator (p-biphenol, PBP). The AFB1 aptamer was immobilized on the AuNPs/Ni-MOF and then hybridized with the complementary DNA (cDNA). PBP was intercalated within the double helix of the cDNA-aptamer. The difference between electrochemical responses of intercalated PBP before and after incubation of AFB1 with the immobilized aptamer was considered as an analytical response. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to monitor the construction processes of the aptasensor. By recording the differential pulse voltammograms of PBP in phosphate buffer (pH 7.0, 0.1M), the linear range and the detection limit of AFB1 were found to be 5.0 × 10-3-150.0ngmL-1 and 1.0 × 10-3ngmL-1 (S/N = 3), respectively. Finally, the designed aptasensor has been successfully used to measure AFB1 in a rice flour sample with satisfying results. Schematic illustrated the different steps of constructing the electrochemical aptasensor based on Au nanoparticles decorated on Ni-metal-organic framework nanosheets and p-biphenol electroactive label for measuring aflatoxin B1 (AFB1).

Voltammetric Immunosensor to Track a Major Peanut Allergen (Ara h 1) in Food Products Employing Quantum Dot Labels.

Tracking unreported allergens in commercial foods can avoid acute allergic reactions. A 2-step electrochemical immunosensor was developed for the analysis of the peanut allergen Ara h 1 in a 1-h assay (<15 min hands-on time). Bare screen-printed carbon electrodes (SPCE) were used as transducers and monoclonal capture and detection antibodies were applied in a sandwich-type immunoassay. The short assay time was achieved by previously combining the target analyte and the detection antibody. Core/shell CdSe@ZnS Quantum Dots were used as electroactive label for the detection of the immunological interaction by differential pulse anodic stripping voltammetry. A linear range between 25 and 1000 ng·mL−1 (LOD = 3.5 ng·mL−1), an adequate precision of the method (Vx0 ≈ 6%), and a sensitivity of 23.0 nA·mL·ng−1·cm−2 were achieved. The immunosensor was able to detect Ara h 1 in a spiked allergen-free product down to 0.05% (m/m) of peanut. Commercial organic farming cookies and cereal and protein bars were tested to track and quantify Ara h 1. The results were validated by comparison with an ELISA kit.

Electrochemical Affinity Assays/Sensors: Brief History and Current Status.

The advent of electrochemical affinity assays and sensors evolved from pioneering efforts in the 1970s to broaden the field of analytes accessible to the selective and sensitive performance of electrochemical detection. The foundation of electrochemical affinity assays/sensors is the specific capture of an analyte by an affinity element and the subsequent transduction of this event into a measurable signal. This review briefly covers the early development of affinity assays and then focuses on advances in the past decade. During this time, progress on electroactive labels, including the use of nanoparticles, quantum dots, organic and organometallic redox compounds, and enzymes with amplification schemes, has led to significant improvements in sensitivity. The emergence of nanomaterials along with microfabrication and microfluidics technology enabled research pathways that couple the ease of use of electrochemical detection for the development of devices that are more user friendly, disposable, and employable, such as lab-on-a-chip, paper, and wearable sensors.

Metal Nanoparticle and Quantum Dot Tags for Signal Amplification in Electrochemical Immunosensors for Biomarker Detection

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags are overviewed, focusing on recent developments in the ultrasensitive detection of biomarkers. MNPs and Qdots can be used separately or in combination with other nanostructures, while performing the function of nanocarriers, electroactive labels, or catalysts. Thus, different functions of MNPs and Qdots as well as recent advances in electrochemical signal amplification are discussed. Additionally, the methods most often used for antibody immobilization on nanoparticles, immunoassay formats, and electrochemical methods for indirect biomarker detection are overviewed.