Bio-bar-code-based photoelectrochemical immunoassay for sensitive detection of prostate-specific antigen using rolling circle amplification and enzymatic biocatalytic precipitation

Advances in prostate specific antigen biosensors-impact of nanotechnology

Prostate cancer is one of the most dangerous and deadly cancers in elderly men. Early diagnosis using prostate-specific antigen (PSA) facilitates disease detection, management and treatment. Biosensors have recently been used as sensitive, selective, inexpensive and rapid diagnostic tools for PSA detection. In this review, a variety of PSA biosensors such as aptasensors, peptisensors and immunesensors are highlighted. These use aptamers, peptides and antibodies in the biorecognition element, respectively, and can detect PSA with very high sensitivity via electrochemical, electrochemiluminescence, fluorescence and surface-enhanced Raman spectroscopy. To improve the sensitivity of most of these PSA biosensors, different nanostructured materials have played a critical role.

Gold Nanoparticles in Conjunction with Nucleic Acids as a Modern Molecular System for Cellular Delivery

Development of nanotechnology has become prominent in many fields, such as medicine, electronics, production of materials, and modern drugs. Nanomaterials and nanoparticles have gained recognition owing to the unique biochemical and physical properties. Considering cellular application, it is speculated that nanoparticles can transfer through cell membranes following different routes exclusively owing to their size (up to 100 nm) and surface functionalities. Nanoparticles have capacity to enter cells by themselves but also to carry other molecules through the lipid bilayer. This quality has been utilized in cellular delivery of substances like small chemical drugs or nucleic acids. Different nanoparticles including lipids, silica, and metal nanoparticles have been exploited in conjugation with nucleic acids. However, the noble metal nanoparticles create an alternative, out of which gold nanoparticles (AuNP) are the most common. The hybrids of DNA or RNA and metal nanoparticles can be employed for functional assemblies for variety of applications in medicine, diagnostics or nano-electronics by means of biomarkers, specific imaging probes, or gene expression regulatory function. In this review, we focus on the conjugates of gold nanoparticles and nucleic acids in the view of their potential application for cellular delivery and biomedicine. This review covers the current advances in the nanotechnology of DNA and RNA-AuNP conjugates and their potential applications. We emphasize the crucial role of metal nanoparticles in the nanotechnology of nucleic acids and explore the role of such conjugates in the biological systems. Finally, mechanisms guiding the process of cellular intake, essential for delivery of modern therapeutics, will be discussed.

Introducing graphitic carbon nitride nanosheets as supersandwich-type assembly on porous electrode for ultrasensitive electrochemiluminescence immunosensing

Biomarkers in blood or tissue provide essential information for clinical screening and early disease diagnosis. However, increasing the sensitivity of detecting biomarkers remains a major challenge in a wide variety of electrochemical immunoassays. Herein, we present an electrochemiluminescence (ECL) immunosensing strategy with 1: Nⁿ amplification ratio (target-to-signal probe) for biomarkers detection on a porous gold electrode. The high porosity of the electrode surface provides enough bonding sites for capturing the target biomolecules and thus many DNA labels can be introduced. On the basis of this concept, a great number of graphitic carbon nitride (g-C₃N₄) nanosheets are employed to create a supersandwich-type assembly on a porous electrode via the DNA hybridization process. Furthermore, compared with the traditional sandwich immunoassay (the ratio of target-to-signal probe is 1 : 1), the supersandwich construction can introduce a large number of signal probes, thus resulting in a highly improved sensitivity. The proposed ECL immunosensor exhibits an excellent performance in a concentration range from 0.01 fg mL^-1 to 1 μg mL^-1 with an ultralow detection limit of 0.001 fg mL^-1 (S/N = 3) and excellent selectivity. This sensing strategy could be developed into a real-time assay for the disease-related molecular targets, with many practical applications in biotechnology and life science.

Bio-barcode detection technology and its research applications: A review

With the rapid development of nanotechnology, the bio-barcode assay (BCA), as a new diagnostic tool, has been gradually applied to the detection of protein and nucleic acid targets and small-molecule compounds. BCA has the advantages of high sensitivity, short detection time, simple operation, low cost, good repeatability and good linear relationship between detection results. However, bio-barcode technology is not yet fully formed as a complete detection system, and the detection process in all aspects and stages is unstable. Therefore, studying the optimal reaction conditions, optimizing the experimental steps, exploring the multi-residue detection of small-molecule substances, and preparing immuno-bio-barcode kits are important research directions for the standardization and commercialization of BCA. The main theme of this review was to describe the principle of BCA, provide a comparison of its application, and introduce the single-residue and multi-residue detection of macromolecules and single-residue detection of small molecules. We also compared it with other detection methods, summarized its feasibility and limitations, expecting that with further improvement and development, the technique can be more widely used in the field of stable small-molecule and multi-residue detection.

A novel electrochemical DNA biosensor for transgenic soybean detection based on triple signal amplification

A novel electrochemical DNA biosensor was developed and MON89788 of soybean transgenic gene sequence was detected based on a strategy of rolling circle amplification (RCA) and gold nanoparticle cube (AuNPC)-labeled multiple probes. First, the mercapto-modified capture DNA was immobilized on the surface of the Fe3O4@Au magnetic nanoparticles via an Au-S bond, and the capture DNA was opened and complementarily hybridized with the target DNA to form a double-stranded DNA. In the 10 × reaction buffer, Exonuclease III (ExoIII) specifically recognized and sheared the double-stranded DNA to release the target DNA, which led to the next round of reaction. Afterward, AuNP cube-loaded ssDNA (AuNPC/DNA) was added with the rolling circle reaction with the help of Phi29 DNA polymerase and T4 ligase. Finally, [Ru(NH3)6]3+ was attracted directly by the anionic phosphate of ssDNA via electrostatic interaction. The determination was carried out by using chronocoulometry (CC), and the CC signal was recorded. The mass amount of DNA strands extended infinitely on the AuNPs cube and numerous [Ru(NH3)6]3+ were absorbed, thus the detected signal was highly amplified. The corresponding CC signal showed a good linear relationship with the logarithm of the target DNA concentration in the range of 1 × 10-16 to 1 × 10-7 mol L-1, with a detection limit of 4.5 × 10-17 mol L-1. Specific gene sequence of MON89788 in soybean samples was determined, and the recoveries ranged from 97.3% to 102.0%. This sensor is one of the most sensitive sensors for genetic sequence assessment at present. Moreover, it demonstrates good selectivity, stability, and reproducibility.

Target-induced formation of multiple DNAzymes in solid-state nanochannels: Toward innovative photoelectrochemical probing of telomerase activity

Solid-state nanochannels have great potentials in the vibrant field of photoelectrochemical (PEC) bioanalysis. This work herein demonstrates the innovative use of DNA-decorated nanoporous anodic alumina (NAA) nanochannels for sensitive PEC bioanalysis of telomerase (TE) activity. Specifically, telomerase primer sequences (TS) were initially immobilized within the NAA nanochannels and then extended by TE in the presence of deoxyribonucleoside triphosphates (dNTPs). The as formed single-strand DNA was then directed to hybrid with many partially matched single-strand assisting DNA (aDNA), leading to the formation of multiple DNAzymes by the unmatched parts and the subsequent DNAzyme-stimulated biocatalytic precipitation (BCP) within the nanochannels. Because the inhibited signals of the photoelectrode could be correlated with TE-enabled TS extension, an innovative nanochannels PEC bioanalysis could be realized for probing TE activity. This work features the ingenious use of DNA-associated nanochannels for PEC bioanalysis of TE activity. Given the versatile functions of DNA molecules, the extension of this strategy easily allows for addressing numerous other targets of interest. Also, we envision this work could inspire more interest for the further development of nanochannels PEC bioanalysis.

Impact of conjugation strategies for targeting of antibodies in gold nanoparticles for ultrasensitive detection of 17β-estradiol

Antibody-coated nanoparticles have recently attracted considerable attention, with the focus falling on diagnostics. Nevertheless, controlled antibody bioconjugation remains a challenge. Here, we present two strategies of bioconjugation with the aim of evaluating the best approach for the coupling of antibodies on the surface of nanomaterials in an oriented way. We employed electrostatic interaction (physical adsorption) and covalent conjugation in the orientation of antibodies on the metallic surface as coupling methods, and their influence on the detection of 17β-estradiol was addressed with localized surface plasmon resonance. The understanding of these mechanisms is fundamental for the development of reproducible inorganic bioconjugates with oriented surface as well sensibility of immunoassays.

Affinity-Based Detection of Biomolecules Using Photo-Electrochemical Readout

Detection and quantification of biologically-relevant analytes using handheld platforms are important for point-of-care diagnostics, real-time health monitoring, and treatment monitoring. Among the various signal transduction methods used in portable biosensors, photoelectrochemcial (PEC) readout has emerged as a promising approach due to its low limit-of-detection and high sensitivity. For this readout method to be applicable to analyzing native samples, performance requirements beyond sensitivity such as specificity, stability, and ease of operation are critical. These performance requirements are governed by the properties of the photoactive materials and signal transduction mechanisms that are used in PEC biosensing. In this review, we categorize PEC biosensors into five areas based on their signal transduction strategy: (a) introduction of photoactive species, (b) generation of electron/hole donors, (c) use of steric hinderance, (d) in situ induction of light, and (e) resonance energy transfer. We discuss the combination of strengths and weaknesses that these signal transduction systems and their material building blocks offer by reviewing the recent progress in this area. Developing the appropriate PEC biosensor starts with defining the application case followed by choosing the materials and signal transduction strategies that meet the application-based specifications.

Ultrasensitive electroluminescence biosensor for a breast cancer marker microRNA based on target cyclic regeneration and multi-labeled magnetized nanoparticles

An electrochemiluminescent (ECL) biosensor is described for the determination of the breast cancer biomarker microRNA. The method is based on the amplification via target cyclic regeneration through a system of hairpin DNA probes, primers, and Klenow fragment of DNA polymerases combined with CdTe quantum dots (QDs) and gold nanoparticles. The assay is performed by exploiting the luminescence properties of CdTe-QDs and K₂S₂O₈ as a co-reactive agent to increase the ECL signal. It was successfully applied to ECL-based detection of a 20-mer microRNA. The sensor has a linear response in the 0.1 fM to 0.2 pM microRNA concentration range and a detection limit as low as 33 aM. The assay has been applied to the determination of microRNA spiked in serum samples, and recoveries ranged from 94.4 to 100.5%. Graphical abstract A novel electroluminescence biosensor based on the amplification of target cyclic regeneration is described. It is achieved by using a system of hairpin DNA probes, primers, and Klenow fragment of DNA polymerases combined with CdTe QDs and Au NPs, and was successfully applied to microRNA detection.

Beta-cyclodextrin-functionalized CdS nanorods as building modules for ultrasensitive photoelectrochemical bioassay of HIV DNA

Nowadays, acquired immunodeficiency syndrome has become a formidable danger to human health, and its early diagnosis is urgent need with the increasing quantity of patients around the world. Herein, we first synthesized beta-cyclodextrin-functionalized CdS nanorods (β-CD@CdS NRs) with high stability and desirable photo-electricity activity, and served as easy-to-assemble building modules to design a novel photoelectrochemical biosensor for human immune deficiency virus (HIV) DNA detection by coupling with catalytic hairpin assembly (CHA)-mediated biocatalytic precipitation and the host-guest interaction between adamantine (ADA) and β-CD. In the presence of HIV DNA, CHA process was triggered with the aid of hairpin DNA1 and ADA-labelled hairpin DNA2, and then generated large amounts of G-quadruplex, which could be formed hemin/G-quadruplex DNAzyme to catalyze 4-chloro-1-naphthol to generate insoluble precipitation on photoelectrode surface, followed by the decreased photocurrent response due to the corresponding stereo-hindrance effect. Under optimized conditions, this biosensor exhibited wide linear dynamic range (10 fM - 1 nM) and low detection limit of 1.16 fM, as well as high sensitivity, excellent stability, and satisfactory feasibility in human-serum samples. Moreover, the prepared β-CD@CdS NRs could be applied to the construction of other advanced sensing platform, showing great prospect in clinical diagnostics.

Low level of Cyclin-D1 correlates with worse prognosis of clear cell renal cell carcinoma patients

Cyclin-D1 (CCND1) belongs to the highly conserved cyclin family whose members are characterized by abundant expression during the cell cycle. As an oncogene, high level of CCND1 was observed and related to poor prognosis and tumor recurrence in many cancers. In this study, we focused on the role of CCND1 in the clinical outcome of clear cell renal cell carcinoma (ccRCC). Gene Expression Omnibus database, The Cancer Genome Atlas database, and immunohistochemical staining were used. The mRNA and protein levels of CCND1 were significantly enhanced in ccRCC tumor tissues. However, the low level of CCND1, but not high level of CCND1, was related to poor prognosis and tumor recurrence in ccRCC. Further analysis showed that CCND1 mRNA level decreased with increasing ccRCC tumor grades and the rate of recurrence in ccRCC patients. In a nomogram model, the CCND1 mRNA level was shown to help predict ccRCC patient recurrence. CCND1 is a strong determinant for prediction of recurrence. The patients with high CCND1 level appear to have a more favorable prognosis together with more frequent low-grade tumors and low rate of recurrence. This is the first study to investigate the prognostic roles of CCND1 in ccRCC and discovered that CCND1 had an unconventional positive impact on the clinical outcome of ccRCC patients.

Novel 3D Printed Device for Dual-Signaling Ratiometric Photoelectrochemical Readout of Biomarker Using λ-Exonuclease-Assisted Recycling Amplification

A ratiometric photoelectrochemical (PEC) sensing strategy was proposed for monitoring of carcinoembryonic antigen (CEA) based on a homemade 3D printing device with dual-working photoelectrodes (PE₁ and PE₂), coupling λ-exonuclease (λ-Exo)-assisted recycling amplification with CdS quantum dots. Gold nanoparticles-functionalized ZnO nanorods were utilized as PEC substrate for generating initial photocurrent and immobilizing DNA probe. Upon incubation of target with DNA trigger/CEA aptamer-modified magnetic bead (tri/apt-MB), DNA trigger dissociated from magnetic bead and then hybridized with capture probe (cp) on PE₁ or opened hairpin probe (hp) on PE₂ to form double-stranded DNA (dsDNA). The exonuclease could recognize and cleave two newly generated dsDNA, leading to the release of trigger. The free trigger strand continued to hybridize with the remaining cp/hp, which were cleaved by λ-Exo, and then trigger was released again and restarted next recycle with the λ-Exo. After digestion of λ-Exo, the number of capture probes on PE₁ was reduced, and many short DNA fragments were produced on PE₂, thereby resulting in the decreasing CdS QDs on PE₁ and the increasing CdS QDs on PE₂. As a result, it was observed that the ratio value of photocurrents (PE₁/PE₂) significantly decreased with the increasing CEA. Under optimum conditions, the sensing method showed a good linear relationship toward CEA within the dynamic range of 0.02-10 ng mL^-1 and a detection limit of 6.0 pg mL^-1. Moreover, the ratiometric PEC sensor exhibited good reproducibility, satisfying stability, and remarkable anti-interference performance, which suggests its promising application prospect to detect target CEA.

Metallic Fe-Au Barcode Nanowires as a Simultaneous T Cell Capturing and Cytokine Sensing Platform for Immunoassay at the Single-Cell Level

Barcode nanowires (BNWs) composed of multiple layered segments of different materials are attractive to bioengineering field due to their characteristics that allow the adjustment of physicochemical properties and conjugation with two or more types of biomolecules to facilitate multiple tasks. Here, we report a metallic Fe (iron)-Au (gold) BNW-based platform for capturing CD8 T cells and the interferon-γ (γ) they secrete, both of which play key roles in controlling infectious diseases such as tuberculosis, at the single-cell level. We also describe an efficient approach for conjugating distinct antibodies, which recognize different epitopes to appropriate materials. The platform achieved detection even with 4.45-35.6 μg mL^-1 of BNWs. The T cell capture efficiency was close to 100% and the detection limit for interferon-γ was 460 pg mL^-1. This work presents a potential guideline for the design of single-cell immunoassay platforms for eliminating diagnostic errors by unambiguously identifying disease-relevant immune mediators.

A dandelion-like liposomes-encoded magnetic bead probe-based toehold-mediated DNA circuit for the amplification detection of MiRNA

The development of facile and sensitive miRNA quantitative detection methods is a central challenge for the early diagnosis of miRNA-related diseases. Herein, we propose a strategy for a liposome-encoded magnetic bead-based DNA toehold-mediated DNA circuit for the simple and sensitive detection of miRNA based on a toehold-mediated circular strand displacement reaction (TCSDR) coupled with a personal glucometer (PGM ). In this strategy, a glucoamylase-encapsulated liposomes (GELs)-encoded magnetic bead (GELs-MB) probe is designed to integrate target binding, magnetic separation, and signal response. Upon sensing the target miRNA-21, a GELs-MB probe-based toehold-mediated circular strand displacement reaction (TCSDR) was initiated with the help of fuel-DNA, constructing a DNA circuit system, and realizing target recycling amplification and the disassembly of the liposomes. The disassembled liposomes were finally removed via magnetic separation, and the encapsulated glucoamylase was liberated to catalyze amylose hydrolysis with multiple turnovers to glucose for a PGM readout. Benefiting from target recycling amplification initiated by the toehold-mediated DNA circuit and the liposome multiple-label amplification, a small quantity of target miRNA-21 can be transformed into a large glucose signal. The strategy realized the quantification of miRNA-21 down to a level of 0.7 fM without enzymatic amplification or precise instrumentation. Moreover, the high-density GELs-MB probe allows the sensitive detection of miRNA-21 to be accomplished within 1.5 h. Furthermore, this strategy exhibits the advantages of specificity and simplicity, since a toehold-mediated strand displacement reaction, magnetic separation and portable PGM were used. Importantly, this strategy has been demonstrated to allow the high-confidence quantification of miRNA. Therefore, with the advantages of low cost, ease of use, portability, and sensitivity, the reported method holds great potential for the early diagnosis of miRNA-related diseases.

A sandwich-type electrochemical aptasensor for the carcinoembryonic antigen via biocatalytic precipitation amplification and by using gold nanoparticle composites

A sandwich-type electrochemical aptasensor is described for detecting the carcinoembryonic antigen (CEA) with high sensitivity and accuracy. Two kinds of nanomaterials are used. The first was obtained by modifying gold nanoparticles with reduced graphene oxide and hemin (Hemin-rGO-AuNPs). The second consists of horseradish peroxidase-modified organic-inorganic hybrid nanoflowers linked to gold nanoparticles to obtain an architecture of type HRP-Cu₃(PO₄)₂-HNF-AuNPs). These serve as carriers for two aptamers (apt1 and apt2) against CEA. Simultaneously, they were used to catalyze the precipitation reaction between 4-chloro-1-naphthol(4-CN) and H₂O₂. A sandwich-type assay linked to enzyme inhibition amplification was established for electrochemical determination of CEA. Under optimal experimental conditions and by using differential pulse voltammetry, the response peak currents (best measured at -0.34 V vs. Ag/AgCl) increases linearly with the logarithm of the CEA concentration in the range between 100 fg mL^-1 and 100 ng mL^-1. The detection limit is as low as 29 fg mL^-1. Graphical abstract Schematic representation of the sandwich-type electrochemical aptasensor based on signal inhibition amplification from biocatalytic precipitation reaction. (HRP-Cu₃(PO₄)₂ hybrid nanoflowers: Horseradish Peroxidase-Cu₃(PO₄)₂ hybrid nanoflowers; AuNPs: Gold Nanoparticles; Hemin-rGO-AuNPs: Hemin-Reduced Graphene Oxide-Gold Nanoparticles; BSA: Bovine Serum Albumin; CEA: Carcinoembryonic Antigen; CEA_apt1: 5'-SH-(CH₂)₆-ATA CCA GCT TAT TCA ATT-3'; CEA_apt2: 5'-NH₂-(CH₂)₆-AGG GGG TGA AGG GAT ACC C-3'; GCE: Glassy carbon electrode; 4-CN: 4-Chloro-1-naphthol; DPV: Differential pulse voltammetry).

Emerging ultrafast nucleic acid amplification technologies for next-generation molecular diagnostics

Over the last decade, nucleic acid amplification tests (NAATs) including polymerase chain reaction (PCR) were an indispensable methodology for diagnosing cancers, viral and bacterial infections owing to their high sensitivity and specificity. Because the NAATs can recognize and discriminate even a few copies of nucleic acid (NA) and species-specific NA sequences, NAATs have become the gold standard in a wide range of applications. However, limitations of NAAT approaches have recently become more apparent by reason of their lengthy run time, large reaction volume, and complex protocol. To meet the current demands of clinicians and biomedical researchers, new NAATs have developed to achieve ultrafast sample-to-answer protocols for the point-of-care testing (POCT). In this review, ultrafast NA-POCT platforms are discussed, outlining their NA amplification principles as well as delineating recent advances in ultrafast NAAT applications. The main focus is to provide an overview of NA-POCT platforms in regard to sample preparation of NA, NA amplification, NA detection process, interpretation of the analysis, and evaluation of the platform design. Increasing importance will be given to innovative, ultrafast amplification methods and tools which incorporate artificial intelligence (AI)-associated data analysis processes and mobile-healthcare networks. The future prospects of NA POCT platforms are promising as they allow absolute quantitation of NA in individuals which is essential to precision medicine.

Gold Nanoparticle-Induced Photocurrent Quenching and Recovery of Polymer Dots: Toward Signal-On Energy-Transfer-Based Photocathodic Bioanalysis of Telomerase Activity in Cell Extracts

Energy transfer (ET) in photoelectrochemical (PEC) bioanalysis is usually generated between noble metal nanoparticles (NPs) and traditional inorganic quantum dots (QDs). Using the innovative polymer dot (Pdot)-involved ET, this work reports the first signal-on and cathodic PEC bioanalysis toward telomerase (TE) activity in cell extracts. Specifically, the sequential binding of capture DNA (cDNA), telomerase primer sequence (TS), and Au NP-labeled probe DNA (Au NP-pDNA) on the electrode would place the Au NPs in close proximity of the Pdots, leading to obvious quenching of the cathodic photocurrent. The subsequent extension of the TS by TE in the presence of deoxyribonucleoside triphosphates (dNTPs) would then release the Ag NP-pDNA from the electrode, leading to the recovery of the photocurrent. On the basis of the Au NP-induced photocurrent quenching and the recovery of Pdots, a sensitive biosensor could thus be developed by tracking the photocurrents to probe the TE activity. This strategy allows for signal-on and cathodic PEC bioanalysis of TE, which can be easily extended for numerous other targets of interest. We believe this work could offer a new perspective for the rational implementation of Pdot-involved ET for advanced PEC bioanalysis.

Sensitive fluorescent detection of Listeria monocytogenes by combining a universal asymmetric polymerase chain reaction with rolling circle amplification

A new, facile, low-cost, and highly sensitive method for detection of Listeria monocytogenes involving a combination of asymmetric polymerase chain reaction (aPCR) and rolling circle amplification (RCA) had been developed. The aPCR-RCA processes were not new but components of the processes made the assay useful. Twenty-one thymine (21-T) tagged forward primer generated universal twenty-one adenine (21-A) aPCR amplicons after aPCR amplification. A poly-T sequence dumbbell-like RCA template was produced through the blunt-end ligation activity of T4 DNA ligase. After the mixture of aPCR amplicons and dumbbell-like RCA template, the RCA reaction would initiate when the addition of phi29 DNA polymerase, then a large number of G-quadruplex sequences were produced which allowed the intercalation of Thioflavin T (3,6-dimethyl-2-(4-dimethylaminophenyl) benzo-thiazolium cation, THT) for easy fluorescence detection. Under the optimal conditions, the assay showed a limit of detection (LOD) of 4.8 × 10¹ CFU/mL in pure culture and 4.0 × 10² CFU/g in spiked lettuce homogenates. By changing the aPCR primer, the aPCR-RCA method developed in this study had a potential to detect other bacteria without the design an RCA template for each bacterium.

Preparation and identification of chicken egg yolk immunoglobulins against human enterovirus 71 for diagnosis of hand-foot-and-mouth disease

Human enterovirus 71 (EV71) is one of the major pathogens that causes hand-foot-and mouth disease, and there is an urgent need for rapid diagnosis of EV71 virus infection for early antiviral treatment. The aim of this study was to prepare chicken egg yolk immunoglobulin Y (IgY) for the diagnosis of enterovirus type 71 infection. The antibodies were raised by intramuscular immunization of laying hens with inactivated human EV71 and isolated from the egg yolk by multiple steps of polyethylene glycol 6000 extraction. The average concentration of IgY antibody was 26.60 mg/mL during the whole immunization. After the first immunization, the IgY titer gradually increased, and reached the peak on the 55th days. Meanwhile, the use of western blotting test demonstrated that specific IgY binds specifically to capsid proteins VP2 and VP3 of EV71 virus. Furthermore, a facile one-step method based on turn-on fluorescence sensing was developed by using IgY antibodies, which can detect EV71 virus at low concentrations of 10⁴ PFU/mL and was 94.44% coincidence with RT-PCR in 30 clinical samples. These findings indicate that EV71-IgY antibodies are an easily prepared and rich source of antibodies that offers a potential alternative strategy for routine screening of EV71 infection.

Ca2+-Triggered pH-Response Sodium Alginate Hydrogel Precipitation for Amplified Sandwich-Type Impedimetric Immunosensor of Tumor Marker

Signal amplification is of great significance in the ultrasensitive electrochemical impedimetric immunoassays for tumor marker detection. A cascaded signal amplification approach was designed using gold nanoparticle-CaCO₃ microspheres (AuNP-CaCO₃) to trigger pH-responsive alginate hydrogel precipitation for sandwich-type impedimetric immunosensor. AuNP-CaCO₃ exerts a large hindrance effect and can release Ca²⁺ ions under weak acidic conditions, and thus can serve as a multifunctional label. The hindrance effect of AuNP-CaCO₃ can significantly enhance the impedance response as the initial signal amplification. Then, part of CaCO₃ dissolves under weak acid conditions and releases Ca²⁺, which can cross-link with alginate to generate an insoluble alginate hydrogel precipitate on the sensing interface, significantly increasing the impedance signal. The impedance signal can be further amplified by making the hydrogel negatively charged based on the pH-responsive surface charge properties of the alginate hydrogel. Benefiting from the cascaded signal amplification, this impedimetric immunosensor exhibits a linear range from 1.0 fg mL^-1 to 100 ng mL^-1, an detection limit of 0.09 fg mL^-1, and ultrahigh sensitivity of 973.01 Ω (lg(ng mL^-1))^-1 toward the assay of prostate specific antigen (PSA).

A label-free and double recognition-amplification novel strategy for sensitive and accurate carcinoembryonic antigen assay

Herein, a label-free and double recognition-amplification (LDRA) strategy for carcinoembryonic antigen (CEA) detection was developed, based on a new designed dual-function messenger probe (DMP) coalescing with DNA tetrahedron probes (DTPs) and hybridization chain reaction (HCR). The DMP possess dual-function to replace CEA for specific interface hybridization and initiate hybridization chain reaction. The interfacial hybridization event was quantitatively converted to an electrochemical signal by using hemin/G-quadruplex (h-Gx) formed after the hybridization chain reaction. Self-assembled DNA tetrahedron probes, which were readily decorated on an electrode surface as a scaffold with rigid support and ordered orientation, enabled the highly efficient strands hybridization and greatly increased target accessibility as well as significantly decreased noise. The proposed assay integrated dual recognition processes and HCR signal amplification processes, achieving the identification of low concentration of CEA as detection limit of 18.2 fg mL^-1 (S/N = 3) and wider linearity range of 0.0001 ng mL^-1-50 ng mL^-1. A new electrochemical sensing method was proposed for CEA detection and used in real clinical samples. The obtained results were good consistency with those of clinical diagnosis.

A Novel Gold Nanoprobe for a Simple Electrochemiluminescence Determination of a Prostate-specific Antigen Based on a Peptide Cleavage Reaction

A novel gold nanoprobe for a sensitive and simple determination of a prostate-specific antigen (PSA) was designed on the basis of homogeneous detection and a peptide cleavage reaction. The gold nanoprobe (AuNPs-peptide-Ru1) consisted of a specific peptide tagged with a ruthenium(II) complex (Ru1) and gold nanoparticles (AuNPs) conjugated with the peptide via the strong Au-S bond between the AuNPs surface and the thiol group of the peptide. The electrochemiluminescence (ECL) enzymatic-cleavage-reaction-based bioanalytic system based on homogeneous detection has overcome shortcomings from a complicated fabrication process of traditional electrodes. In the presence of the target PSA, it specifically cleaved the peptide of the AuNPs-peptide-Ru1, and the ECL signal substance (Ru1) part dissociated from AuNPs-peptide-Ru1. This resulted in an increase in the ECL intensity. The ECL biosensor could detect PSA concentrations in the range from 1.0 × 10^-12 to 1.0 × 10^-9 g/mL, the detection limit was 4.0 × 10^-13 g/mL. The assay with the advantages of a simple method for PSA was selective and fast. It is superior to the immunoassay, and is a promising strategy to develop biosensors based on enzymatic cleavage including electrochemistry and optics.

Highly sensitive and specific electrochemical biosensor for microRNA-21 detection by coupling catalytic hairpin assembly with rolling circle amplification

BACKGROUND

MicroRNA plays a significant role in gene regulation and is usually regarded as an important biological marker. Electrochemical biosensors are excellent tools for microRNA detection.

METHODS

In this experiment, we take miRNA-21 as a target, combining catalytic hairpin assembly (CHA) and rolling circle amplification (RCA) as a dual signal amplification strategy for the detection of microRNA in an electrochemical biosensor.

RESULTS

This strategy has a good linear range of 0.5-12 500 pmol of microRNA. The limit of detection (LOD) for miRNA is as low as 290 fmol, showing excellent performance. Finally, this method has been successfully applied to the detection of miRNA-21 from HeLa cells.

CONCLUSION

This method can be applied not only for microRNA detection with high sensitivity and speed, but can also detect small molecules and proteins combined with aptamers.

Palindromic Molecular Beacon Based Z-Scheme BiOCl-Au-CdS Photoelectrochemical Biodetection

This work presented an innovative and rationally engineered palindromic molecular beacon (PMB) based "Z-scheme" photoelectrochemical (PEC) biosensing protocol for the selective screening of kanamycin (Kana) through DNA hybridization-induced conformational conversion. Interestingly, the ingeniously designed PMB integrated the multifunctional elements including recognition region, primer-like palindromic fragment, and polymerization-nicking template. The cosensitized structures consisted of CdS quantum dot functionalized hairpin DNA2 (QD-HP2) and region-selectively deposited gold nanoparticles onto {001} facets of bismuth oxychloride (BiOCl-Au). Compared with BiOCl-Au alone, the attachment of CdS QDs onto BiOCl-Au (i.e., BiOCl-Au-CdS QDs) exhibited evidently enhanced photocurrent intensity thanks to the synergistic effect of Z-scheme BiOCl-Au-CdS QDs. After incubation with target Kana, Kana-aptamer binding could induce the exposure of PMB region for hairpin DNA1 (HP1). The exposed palindromic tails hybridized with each other (like a molecular machine) to consume the substrates (dNTPs) and fuels (enzyme) for the releasing of numerous nick fragments (Nick). The as-generated nick fragments could specifically hybridize with the complementary region of QD-HP2, thus resulting in decreasing photocurrent because of the increasing spatial distance for electron transfer between two-type photosensitizers. Under optimum conditions, the PMB-based sensing system exhibited satisfying photocurrent responses toward target Kana within the working range from 50 to 5000 fM at a low detection limit of 29 fM. Impressively, the concept of a palindromic fragment-mediated primer-free biosensing strategy offers a new avenue for advanced development of efficient and convenient biodetection systems.

Glucose oxidase-loaded liposomes forin situamplified signal of electrochemical immunoassay on a handheld pH meter

Methods based on a pH meter have been developed for immunoassays, but most involve low sensitivity and weakly detectable signals, and thus are unsuitable for routine use.

A novel fluorescence immunosensor based on Förster resonance energy transfer between nitrogen and sulfur co-doped carbon dot functionalized silica nanospheres and Au@Ag NPs

A fluorescence immunosensor for PSA detection was developed based on the FRET between Si/NS-CDs and Au@Ag NPs.

Ultrasensitive detection of prostate specific antigen using a personal glucose meter based on DNA-mediated immunoreaction

We report a point-of-care immunosensor coupled with a rolling circle reaction and a personal glucose meter for sensitive detection of PSA.

Photoelectrochemical immunoassay of aflatoxin B1 in foodstuff based on amorphous TiO2 and CsPbBr3 perovskite nanocrystals

A split-type photoelectrochemical immunoassay was designed to detect AFB₁ in foodstuffs using amorphous TiO₂ and CsPbBr₃ perovskite nanocrystals.

An acid-responsive all-in-one signal amplification strategy for the ultrasensitive prostate-specific antigen detection

A one-pot strategy for the preparation of all-in-one signal tags for the colorimetric immunoassay of prostate-specific antigen.