Bioresponsive Release System for Visual Fluorescence Detection of Carcinoembryonic Antigen from Mesoporous Silica Nanocontainers Mediated Optical Color on Quantum Dot-Enzyme-Impregnated Paper

Analytical performance of newly developed rapid point-of-care test for the simultaneous detection of hepatitis A, B, and C viruses in serum samples

ABSTRACTBACKGROUND

Although immunoassays play a major role in the detection of hepatitis viruses, there is a need for a point-of-care (POC) test. We evaluated the EuDx-HE (A,B,C) kit (EUDIPIA, Cheongju, Korea), which detects anti-hepatitis A virus (HAV) immunoglobulin M (IgM), hepatitis B virus surface antigen (HBsAg), and anti-hepatitis C virus (HCV) immunoglobulin G (IgG) simultaneously using an immunochromatographic method within 15 minutes.

METHODS

A total of 1581 serum samples including 57, 477, and 451 samples positive for anti-HAV IgM, HBsAg, and anti-HBV IgG, respectively, were analyzed. We investigated the diagnostic accuracy of the EuDx-HE (A,B,C) kit by comparison with SD BIOLINE POC kits (Abbott, Chicago, IL) using Architect immunoassays as a reference method.

RESULTS

For anti-HAV IgM and HBsAg detection, the EuDx-HE (A,B,C) kit showed a higher sensitivity and a slightly lower specificity than the SD BIOLINE kit. For anti-HCV IgG detection, the EuDx-HE (A,B,C) kit had a higher sensitivity and a higher specificity than the SD BIOLINE kit. The agreement for positivity between the POC tests was >89.47%, with κ values of 0.844, 0.941, and 0.943 for HAV, HBV, and HCV, respectively.

CONCLUSION

The EuDx-HE (A,B,C) kit showed an acceptable clinical performance for detecting anti-HAV IgM, HBsAg, and anti-HCV.

The design, fabrication, and applications of flexible biosensing devices

Flexible biosensors form part of a rapidly growing research field that take advantage of a multidisciplinary approach involving materials, fabrication and design strategies to be able to function at biological interfaces that may be soft, intrinsically curvy, irregular, or elastic. Numerous exciting advancements are being proposed and developed each year towards applications in healthcare, fundamental biomedical research, food safety and environmental monitoring. In order to place these developments in perspective, this review is intended to present an overview on field of flexible biosensor development. We endeavor to show how this subset of the broader field of flexible and wearable devices presents unique characteristics inherent in their design. Initially, a discussion on the structure of flexible biosensors is presented to address the critical issues specific to their design. We then summarize the different materials as substrates that can resist mechanical deformation while retaining their function of the bioreceptors and active elements. Several examples of flexible biosensors are presented based on the different environments in which they may be deployed or on the basis of targeted biological analytes. Challenges and future perspectives pertinent to the current and future stages of development are presented. Through these summaries and discussion, this review is expected to provide insights towards a systematic and fundamental understanding for the fabrication and utilization of flexible biosensors, as well as inspire and improve designs for smart and effective devices in the future.

Phytic acid-based copper(ii) ion-selective electrode on graphene oxide for potentiometric immunoassay of breast cancer antigen 15-3

A potentiometric immunoassay based on a copper(ii) ion-selective electrode (Cu-ISE) was designed for the quantitative determination of carbohydrate antigen 15-3 (CA 15-3; a tumor marker associated with breast cancer).

Chitosan–gold nanocomposite and its functionalized paper strips for reversible visual sensing and removal of trace Hg2+ in practice

To eliminate mercury contamination in aqueous environment, chitosan–gold nanocomposite and its functionalized paper strips were designed and developed for visual sensing and removal of trace Hg²⁺.

Magneto-controlled flow-injection device for electrochemical immunoassay of alpha-fetoprotein on magnetic beads using redox-active ferrocene derivative polymer nanospheres

A new electrochemical immunosensing protocol by coupling with a magneto-controlled flow-through microfluidic device was developed for the sensitive detection of alpha-fetoprotein (AFP) on magnetic beads (MB) using ferrocene derivative polymer nanospheres (FDNP) as the electroactive mediators.

Conductometric immunoassay of alpha-fetoprotein in sera of liver cancer patients using bienzyme-functionalized nanometer-sized silica beads

A conductometric immunoassay protocol was designed for the sensitive detection of a liver cancer biomarker, alpha-fetoprotein (AFP), in biological fluids by using enzyme-conjugated nanometer-sized enzyme-doped silica beads.

A turn-on fluorescent probe for sensitive detection of ascorbic acid based on SiNP–MnO2nanocomposites

A nanoprobe prepared by coupling nanoparticles (SiNPs) with BSA templated-MnO₂nanosheets was constructed for ascorbic acid analysis.

g-C3N4 nanosheet-based ratiometric fluorescent probes for the amplification and imaging of miRNA in living cells

By using BCNNS as a nanocarrier, a fluorescence quencher and an interior label, and using CuNC-labeled hairpin DNA for dual-signal output, a dual-emission ratiometric fluorescent probe was fabricated for the measurement of intracellular miRNA.

A simple functionalized silica microsphere for fast PETN vapor detection based on fluorescence color changes via a catalyzed oxidation process

A fluorene substituted vinyl-SiO microsphere performs a rapid fluorescence color change via oxidation with highly selective PETN catalysis.

Construction of Acetaldehyde-Modified g-C3N4 Ultrathin Nanosheets via Ethylene Glycol-Assisted Liquid Exfoliation for Selective Fluorescence Sensing of Ag. ACS APPLIED MATERIALS & INTERFACES 2018;10:44624-44633. [PMID: 30511564 DOI: 10.1021/acsami.8b15501]

We successfully prepared acetaldehyde-modified graphitic carbon nitride (g-C₃N₄) ultrathin nanosheets (ACNNSs) by a simple ethylene glycol-assisted liquid exfoliation method. The introduction of acetaldehyde regulated the surface energy of g-C₃N₄ to better match with that of water, which improved the exfoliation efficiency. Moreover, acetaldehyde introduces defects into the g-C₃N₄ structure, which can act as excitation energy traps and cause considerable variation in the fluorescence emission. Benefiting from the stable photoluminescence emission, good water solubility, and biocompatibility, the obtained ACNNSs showed a selective fluorescent response to Ag⁺ in both aqueous solution and living cells. The strong absorption and intimate contact with Ag⁺ and its appropriate redox potential of ACNNSs contributed to this excellent fluorescent response. A simple and environmental friendly approach was proposed to simultaneously achieve modification and exfoliation of g-C₃N₄ in aqueous solution. These findings might lead to wider applications of carbon-based nanomaterials as active materials for fluorescence detection in the environment.

Aptamer Conformation Switching-Induced Two-Stage Amplification for Fluorescent Detection of Proteins

Basing on the conformation change of aptamer caused by proteins, a simple and sensitive protein fluorescent assay strategy is proposed, which is assisted by the isothermal amplification reaction of polymerase and nicking endonuclease. In the presence of platelet-derived growth factor (PDGF-BB), the natural conformation of a DNA aptamer would change into a Y-shaped complex, which could hybridize with a molecular beacon (MB) and form a DNA duplex, leading to the open state of the MB and generating a fluorescence signal. Subsequently, with further assistance of isothermal recycling amplification strategies, the designed aptamer sensing platform showed an increment of fluorescence. As a benefit of this amplified strategy, the limit of detection (LOD) was lowered to 0.74 ng/mL, which is much lower than previous reports. This strategy not only offers a new simple, specific, and efficient platform to quantify the target protein in low concentrations, but also shows a powerful approach without multiple washing steps, as well as a precious implementation that has the potential to be integrated into portable, low-cost, and simplified devices for diagnostic applications.

A novel electrochemical immunoassay for carcinoembryonic antigen based on glucose oxidase-encapsulated nanogold hollow spheres with a pH meter readout

A portable electrochemical immunosensing protocol was designed for the sensitive detection of a disease-related tumor biomarker (carcinoembryonic antigen, CEA, used in this case) on a pH meter using glucose oxidase (GOx)-encapsulated gold hollow microspheres (AuHMs) for signal amplification. The assay was carried out on a monoclonal anti-CEA capture antibody-coated microplate with a sandwich-type reaction mode. The GOx-entrapped AuHM was first synthesized using the reverse micelle method and then used as the signal-generation tag for the labeling of polyclonal anti-CEA detection antibody. Accompanying the formation of the sandwiched immunocomplexes, the loaded GOx molecules in the microsphere could catalyze glucose into gluconic acid and hydrogen peroxide. The as-produced gluconic acid changed the microenvironment of the detection solution, thus resulting in the shift of the pH value, which could be quantitatively determined on a portable pH meter. The use of gold hollow microspheres was expected to enhance the loaded amount of GOx for signal amplification. Two labeling protocols including GOx-labeled secondary antibody and GOx-AuHM-labeled secondary antibody were investigated for CEA detection, and improved analytical features were acquired with GOx-AuHM labeling. With the GOx-AuHM labeling strategy, the pH meter-based immunosensing device exhibited a good analytical performance for CEA detection within the dynamic linear range of 0.1-100 ng mL-1 at a detection limit of 0.062 ng mL-1. The strong attachment of anti-CEA antibodies to GOx-AuHM brought a good repeatability and intermediate precision down to 10%. Importantly, no significant differences at the 0.05 significance level were encountered in the analysis of 12 human serum specimens between the developed immunoassay and the commercialized electrochemiluminescent method for CEA determination.

Quantum Dot Based Nano-Biosensors for Detection of Circulating Cell Free miRNAs in Lung Carcinogenesis: From Biology to Clinical Translation

Lung cancer is the most frequently occurring malignancy and the leading cause of cancer-related death for men in our country. The only recommended screening method is clinic based low-dose computed tomography (also called a low-dose CT scan, or LDCT). However, the effect of LDCT on overall mortality observed in lung cancer patients is not statistically significant. Over-diagnosis, excessive cost, risks associated with radiation exposure, false positive results and delay in the commencement of the treatment procedure questions the use of LDCT as a reliable technique for population-based screening. Therefore, identification of minimal-invasive biomarkers able to detect malignancies at an early stage might be useful to reduce the disease burden. Circulating nucleic acids are emerging as important source of information for several chronic pathologies including lung cancer. Of these, circulating cell free miRNAs are reported to be closely associated with the clinical outcome of lung cancer patients. Smaller size, sequence homology between species, low concentration and stability are some of the major challenges involved in characterization and specific detection of miRNAs. To circumvent these problems, synthesis of a quantum dot based nano-biosensor might assist in sensitive, specific and cost-effective detection of differentially regulated miRNAs. The wide excitation and narrow emission spectra of these nanoparticles result in excellent fluorescent quantum yields with a broader color spectrum which make them ideal bio-entities for fluorescence resonance energy transfer (FRET) based detection for sequential or simultaneous study of multiple targets. In addition, photo-resistance and higher stability of these nanoparticles allows extensive exposure and offer state-of-the art sensitivity for miRNA targeting. A major obstacle for integrating QDs into clinical application is the QD-associated toxicity. However, the use of non-toxic shells along with surface modification not only overcomes the toxicity issues, but also increases the ability of QDs to quickly detect circulating cell free miRNAs in a non-invasive mode. The present review illustrates the importance of circulating miRNAs in lung cancer diagnosis and highlights the translational prospects of developing QD-based nano-biosensor for rapid early disease detection.

An enzyme cascade-based electrochemical immunoassay using a polydopamine-carbon nanotube nanocomposite for signal amplification

By coupling tyrosinase (Tyr) and β-galactosidase (Gal) into one redox-cycling scheme, an enzyme cascade-based electrochemical immunosensor with boosted selectivity and sensitivity was constructed using polydopamine-functionalized multiwalled carbon nanotube (MWCNTs-PDA) nanohybrid modified electrodes. The MWCNTs-PDA nanohybrid presented a 5 times enhanced capability for antibody conjugation, which was responsible for signal amplification. In the proposed enzyme cascade scheme, Gal was captured on the immunosensor surface by a sandwiched immunoreaction, which catalyzed phenyl β-d-galactopyranoside (P-GP) into phenol based on a hydrolysis reaction. The resulting phenol was used as a substrate of Tyr, which was catalyzed to catechol and subsequently to o-quinone. The o-quinone was then electrochemically reduced to catechol, forming a redox cycle between catechol and o-quinone. The enzyme cascade-based immunoassay not only significantly amplified the electrochemical signal, but also led to a high selectivity. Taking the detection of CEA as an example, the enzyme cascade-based electrochemical immunosensor showed a detectable range of 10 pg mL^-1 to 10 ng mL^-1 and a low detection limit of 8.39 pg mL^-1 (S/N = 3), which was superior/comparable to those using other methodologies in previous reports. The selectivity of the enzyme cascade-based immunosensor was 44-80% higher than that of a single enzyme-based immunosensor. This work shows great potential of the coupling enzyme cascade in immunosensing for clinical diagnosis with boosted selectivity and sensitivity.

New insights into the structure-performance relationships of mesoporous materials in analytical science

Mesoporous materials are ideal carriers for guest molecules and they have been widely used in analytical science. The unique mesoporous structure provides special properties including large specific surface area, tunable pore size, and excellent pore connectivity. The structural properties of mesoporous materials have been largely made use of to improve the performance of analytical methods. For instance, the large specific surface area of mesoporous materials can provide abundant active sites and increase the probability of contact between analytes and active sites to produce stronger signals, thus leading to the improvement of detection sensitivity. The connections between analytical performances and the structural properties of mesoporous materials have not been discussed previously. Understanding the "structure-performance relationship" is highly important for the development of analytical methods with excellent performance based on mesoporous materials. In this review, we discuss the structural properties of mesoporous materials that can be optimized to improve the analytical performance. The discussion is divided into five sections according to the analytical performances: (i) selectivity-related structural properties, (ii) sensitivity-related structural properties, (iii) response time-related structural properties, (iv) stability-related structural properties, and (v) recovery time-related structural properties.

Structure-Switching Electrochemical Aptasensor for Single-Step and Specific Detection of Trace Mercury in Dairy Products

A reagentless and single-step electrochemical aptasensor with separation-free fashion and rapid response is developed for the Hg²⁺ assay in dairy products. Herein, the sensing strategy is established on Hg²⁺-induced structural transition of the methylene-blue-tagged single-stranded DNA (ssDNA) from a flexible manner to rigid hairpin-shaped double-stranded DNA (dsDNA), generating an improved peak current for the Hg²⁺ assay with a detection limit of 0.62 fM. Importantly, the best signal-to-noise ratio value can be obtained by exploiting Au flowers as sensing material and the optimal ssDNA concentration. The proposed sensor also exhibits high selectivity as a result of the specific thymine-Hg²⁺-thymine (T-Hg²⁺-T) coordination chemistry and can be applied to detect Hg²⁺ in dairy products. With the use of the electric "signal-on" switch, the electrochemical aptasensor has the advantages of simplicity, ease of operation, and high sensitivity and specificity, offering a promising method to assess the safety of dairy products polluted with Hg²⁺.

Microfluidic thread-based electrode system to detect glucose and acetylthiocholine

A reusable and simple to fabricate electrochemical sensor for the detection of glucose and acetylthiocholine using thread-based electrodes and nylon thread is described. The fabrication of the device consisted of two steps. First, three nylon-based electrodes (reference, working, and counter) were painted with one layer of conductive inks (silver and carbon ink, or silver/silver chloride ink). The electrodes were taped onto parafilm, and a piece of white nylon thread was wrapped around each electrode connecting the three electrodes. For the glucose system, a PBS solution containing glucose oxidase (GOx) (10 mg/mL), and potassium ferricyanide (K₃ [Fe(CN)₆ ]) (10 mg/mL) as mediator, was dried onto the thread, and increasing concentrations of glucose (0-15 mM) was added to the thread and measured by cyclic voltammetry (CV). The current output from the glucose oxidation was proportional to the concentration of glucose. For the second system, a solution of acetylcholinesterase (AChE) (0.08 U/mL) in PBS was added to the nylon thread, and increasing concentrations of acetylthiocholine (ATC) (0-9.84 mg/mL) was added and measured by CV. The current output from the oxidation of thiocholine (produced by AChE reacting with ATC) was proportional to the concentrations of ATC added to the thread. From both systems, a graph of current output versus substrate concentration was produced and fitted with a linear regression line that gave R² values of 0.985 (GO_X /glucose) and 0.995 (AChE/ATC).

Nanoarchitectonic-Based Material Platforms for Environmental and Bioprocessing Applications

The challenges of pollution, environmental science, and energy consumption have become global issues of broad societal importance. In order to address these challenges, novel functional systems and advanced materials are needed to achieve high efficiency, low emission, and environmentally friendly performance. A promising approach involves nanostructure-level controls of functional material design through a novel concept, nanoarchitectonics. In this account article, we summarize nanoarchitectonic approaches to create nanoscale platform structures that are potentially useful for environmentally green and bioprocessing applications. The introduced platforms are roughly classified into (i) membrane platforms and (ii) nanostructured platforms. The examples are discussed together with the relevant chemical processes, environmental sensing, bio-related interaction analyses, materials for environmental remediation, non-precious metal catalysts, and facile separation for biomedical uses.

Microwave-Assisted Facile Synthesis of Eu(OH)3 Nanoclusters with Pro-Proliferative Activity Mediated by miR-199a-3p

As a pharmaceutical excipient, dextran serves as an efficient ligand for stabilizing some clinically available inorganic nanomaterials such as iron oxide nanocrystals. Herein, dextran-capped nanosized europium(III) hydroxides [Eu(OH)₃] nanoclusters (NCs) composed of 5 nm Eu(OH)₃ nanoparticles have been large-scale synthesized via a microwave-accelerated hydrothermal reaction. The as-synthesized Eu(OH)₃ NCs exhibited excellent physiological stability and biocompatibility both in vitro and in vivo and possessed considerable pro-proliferative activities in human umbilical vein endothelial cells (HUVECs). To investigate the epigenetic modulation of Eu(OH)₃ NCs-elicited proliferation, the newly developed high-throughput next generation sequencing technology was employed herein. As a result, we have screened 371 dysregulated miRNAs in Eu(OH)₃ NCs-treated HUVECs and obtained 26 potentially functional miRNAs in promoting cell proliferation. Furthermore, upregulated miR-199a-3p was predicted, validated, and eventually confirmed to be a crucial modulator in the pro-proliferative activity of Eu(OH)₃ NCs by targeting zinc fingers and homeoboxes protein 1 (ZHX1). Importantly, these findings provide potential therapeutic strategy for ischemic heart/limb diseases and tissue regeneration by combination of nanomedicine and gene therapy with Eu(OH)₃ NCs and miR-199a-3p-ZHX1 axis modulation.

Upconversion nanocrystal 'armoured' silica fibres with superior photoluminescence for miRNA detection

We have fabricated a flexible membrane, consisting of SiO2 nanofibres armoured with upconversion nanoparticles, exhibiting intense photoluminescence. These assemblies were subsequently grafted with molecular beacons to produce a biosensor suitable for the detection of specific microRNA and with applications in early cancer detection and point-of-care diagnosis.

Applying strand displacement amplification to quantum dots-based fluorescent lateral flow assay strips for HIV-DNA detection

Up to now, the colloidal gold labeling immunochromatographic test strip is a mature and applicable technology. However, different from the conventional gold nanoparticle, quantum dot (QD) possesses larger specific surface area and better biocompatibility. So, as a novel nanomaterial, QD is capable of assembling more biomolecule which could enhance the sensitivity and accuracy of strips by rationality. Besides, strand displacement amplification was drawn into our test strips in this paper, this assumption made HIV-DNA recycling many times and converting it to plentiful QD-dsDNA (double-stranded deoxyribonucleic acid), where after these nano-structures would be captured by test zone. Meanwhile, the suggested scheme eliminated the hook effect owing to the target drop out of the incorporation on test zone, and any nucleotide sequence or substance which has aptamers can work as the target, such as carcinoembryonic antigen or mycotoxin. This assay realized the detection limit of as low as 0.76 pM (S/N = 3) and the detection range of 1 pM to 10 nM. In the end, we made use of this fluorescent lateral flow assay strips with great reproducibility for detecting HIV-DNA in human serum, that attested this method could be applied to practical application prospectively.

An efficient nonlinear hybridization chain reaction-based sensitive fluorescent assay for in situ estimation of calcium channel protein expression on bone marrow cells

A sensitive and highly efficient approach to monitor the expression of proteins on live cells was urgently needed to demonstrate its factor and mechanism and most important for clinical diagnostics and molecular biology. Herein, we developed a simple and highly efficient strategy, nonlinear hybridization chain reaction (nonlinear HCR), for the sensitive determination of proteins on live cells with transient receptor potential vanilloid 4 (TRPV4) and RAW264.7 cells as a model. Unlike the normal hybridization chain reaction (HCR) with multiplicative amplification, an exponential amplified fluorescent response could be obtained in theory based on the proposed nonlinear HCR. As a result, the nonlinear HCR generated a significant enhancement about 3 times compared with the normal HCR and 10 times compared with the directly immunofluorescence assay. Based on the proposed nonlinear HCR, the fluorescent signals increased with the concentration of TRPV4 in the range from 10 pg/mL to 100 ng/mL with a detection limit of 2.8 pg/mL, which would be useful for the sensitive detection of proteins in cell lysis or on cell surface. At the same time, the significant improvements via nonlinear HCR were achieved in the fluorescent imaging system compared with traditional immunofluorescence staining and normal HCR, proving the significant value of nonlinear HCR-based amplification strategy. Success in the establishment of the highly efficient nonlinear HCR strategy offered a simple and sensitive approach to demonstrate the concentration of special proteins on cell and other proteins and nucleotide potentially, revealing a simple and efficient technology for research fields of clinical diagnostics and molecular biology.

Turn-off colorimetric sensor for sequence-specific recognition of single-stranded DNA based upon Y-shaped DNA structure

A novel turn-off colorimetric sensor for sequence-specific recognition of single-stranded DNA (ssDNA) was established by combining Y-shaped DNA duplex and G-quadruplex-hemin DNAzyme. A G-rich single-stranded DNA (Oligo-1) displays peroxidase mimicking catalytic activity due to the specific binding with hemin in the presence of K+, which was able to catalyze the oxidation of colorless 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS2-) by H2O2 to generate green ABTS•- radical for colorimetric assay. Oligonucleotide 2 (Oligo-2) was partly complementary with Oligo-1 and the target DNA. Upon addition of target DNA, Oligo-1, Oligo-2 and target DNA can hybridize with each other to form Y-shaped DNA duplex. The DNAzyme sequence of Oligo-1 was partly caged into Y-shaped DNA duplex, resulting in the inactivation of the DNAzyme and a sharp decrease of the absorbance of the oxidation product of ABTS2-. Under the optimum condition, the absorbance decreased linearly with the concentration of target DNA over the range of 1.0-250 nM and the detection limit was 0.95 nM (3σ/slope) Moreover, satisfied result was obtained for the discrimination of single-base or two-base mismatched DNA.

Quantum Dot-Based FRET Immunoassay for HER2 Using Ultrasmall Affinity Proteins

Engineered scaffold affinity proteins are used in many biological applications with the aim of replacing natural antibodies. Although their very small sizes are beneficial for multivalent nanoparticle conjugation and efficient Förster resonance energy transfer (FRET), the application of engineered affinity proteins in such nanobiosensing formats has been largely neglected. Here, it is shown that very small (≈6.5 kDa) histidine-tagged albumin-binding domain-derived affinity proteins (ADAPTs) can efficiently self-assemble to zwitterionic ligand-coated quantum dots (QDs). These ADAPT-QD conjugates are significantly smaller than QD-conjugates based on IgG, Fab', or single-domain antibodies. Immediate applicability by the quantification of the human epidermal growth factor receptor 2 (HER2) in serum-containing samples using time-gated Tb-to-QD FRET detection on the clinical benchtop immunoassay analyzer KRYPTOR is demonstrated here. Limits of detection down to 40 × 10^-12 m (≈8 ng mL^-1 ) are in a relevant clinical concentration range and outperform previously tested assays with antibodies, antibody fragments, and nanobodies.

Dual-mode fluorescent and colorimetric immunoassay for the ultrasensitive detection of alpha-fetoprotein in serum samples

We present a novel dual-mode fluorescent and colorimetric immunosensor based on conventional immunoassay platforms by utilizing a gold nanoflower (AuNF)-loaded fluorescein molecule (AuNF@Fluorescein) as signal output. The AuNFs were modified with thiolated carboxyl ligand, which consisted of a hydrophobic alkane chain as hydrophobic wallet for fluorescein encapsulation, a tetra (ethylene glycol) unit for biocompatibility and solubility, and a functional carboxyl group for the conjugation of biorecognition molecules for biosensing. The resultant AuNFs showed a high loading capacity of 3.74 × 10⁶ fluorescein molecules per AuNF because of its flower-like shape with many complex branches. By adjusting the solution pH to 8.0, the fluorescein molecules can almost entirely be released from the hydrophobic wallet of AuNF@Fluorescein, which led to strong fluorescent-signal amplification. Under the optimal detection conditions, the proposed immunoassay based on fluorescent signal exhibited ultrahigh sensitivity for alpha-fetoprotein (AFP) detection, with a limit of detection (LOD) of 29 fg/mL. This value is approximately 9.3 × 10³-fold lower than that of corresponding horseradish peroxidase (HRP)-based immunoassay (LOD = 270 pg/mL). The fluorescein molecule also had intrinsic peroxidase-like activity to catalyze 3,3',5,5'-tetramethylbenzidine oxidation with hydrogen peroxide for colorimetric signal. The proposed method with colorimetric mode further exhibited a sensitivity with a LOD of 17.7 pg/mL, which is about 15-fold lower than that of conventional HRP-based immunoassay. The recoveries of the proposed dual-mode immunoassay for AFP spiked serum samples ranged within 89.85%-100.0%, with the coefficient of variations ranging from 0.5% to 2.4%, indicating acceptable accuracy and precision for AFP quantitative detection. The reliability of the developed dual-mode immunoassay was further compared with a commercial chemiluminescence immunoassay kit by analyzing 20 clinical serum samples, showing that the two methods well agreed with each other, with high correlation coefficients of 0.997 and 0.986 based on recorded fluorescence and colorimetric signals, respectively. In summary, the proposed method was highly suitable for the ultrasensitive analysis of biomarkers or infectious diseases by fluorescence mode and can be used for routine clinical diagnosis by colorimetric mode.

An aptamer-based fluorescence bio-sensor for chiral recognition of arginine enantiomers

In this study, a novel aptamer - based fluorescence bio-sensor (aptamer-AuNps) was developed for chiral recognition of arginine (Arg) enantiomers based on aptamer and gold nanoparticles (AuNps). Carboxyfluorescein (FAM) labeled aptamers (Apt) were absorbed on AuNps and their fluorescence intensity could be significantly quenched by AuNps based on fluorescence resonance energy transfer (FRET). Once d-Arg or l-Arg were added into the above solution, the aptamer specifically bind to Arg enantiomers and released from AuNps, so the fluorescence intensity of d-Arg system and l-Arg system were all enhanced. The affinity of Apt to l-Arg is tighter to d-Arg, so the enhanced fluorescence signals of l-Arg system was stronger than d-Arg system. What's more, the enhanced fluorescence were directly proportional to the concentration of d-Arg and l-Arg ranging from 0-300 nM and 0-400 nM with related coefficients of 0.9939 and 0.9952, respectively. Furthermore, the method was successfully applied to detection l-Arg in human urine samples with satisfactory results. Eventually, a simple "OR" logic gate with d-Arg &l-Arg as inputs and AuNps aggregation state as outputs was fabricated, which can help us understand the chiral recognition process deeply.

Ultrasensitive dual probe immunosensor for the monitoring of nicotine induced-brain derived neurotrophic factor released from cancer cells

Brain-derived neurotrophic factor (BDNF) was detected in the extracellular matrix of neuronal cells using a dual probe immunosensor (DPI), where one of them was used as a working and another bioconjugate loading probe. The working probe was fabricated by covalently immobilizing capture anti-BDNF (Cap Ab) on the gold nanoparticles (AuNPs)/conducting polymer composite layer. The bioconjugate probe was modified by drop casting a bioconjugate particles composed of conducting polymer self-assembled AuNPs, immobilized with detection anti-BDNF (Det Ab) and toluidine blue O (TBO). Each sensor layer was characterized using the surface analysis and electrochemical methods. Two modified probes were precisely faced each other to form a microfluidic channel structure and the gap between inside modified surfaces was about 19 µm. At optimized conditions, the DPI showed a linear dynamic range from 4.0 to 600.0 pg/ml with a detection limit of 1.5 ± 0.012 pg/ml. Interference effect of IgG, arginine, glutamine, serine, albumin, and fibrinogene were examined and stability of the developed biosensor was also investigated. The reliability of the DPI sensor was evaluated by monitoring the extracellular release of BDNF using exogenic activators (ethanol, K⁺, and nicotine) in neuronal and non-neuronal cells. In addition, the effect of nicotine onto neuroblastoma cancer cells (SH-SY5Y) was studied in detail.

Proximity aptasensor for protein detection based on an enzyme-free amplification strategy

A novel electrochemical aptasensor for the detection of trace protein is proposed based on proximity binding-induced strand displacement and hybridization chain reaction. This method is proven to be highly selective and has potential practical utility, and offers new opportunities for the convenient detection of proteins with an enzyme-free amplification process.

Editable TiO2 Nanomaterial-Modified Paper in Situ for Highly Efficient Detection of Carcinoembryonic Antigen by Photoelectrochemical Method

In this work, a versatile photoelectrochemical paper-based sensor based on N-carbon dots/TiO₂-Pt-modified paper in situ is developed for sensitive detection of carcinoembryonic antigen (CEA) in clinical serum samples. Interconnected cellulose fibers on paper provide a porous, 3D, and flexible substrate for photoelectrochemical sensing. In situ modification of N-carbon dots/TiO₂-Pt with editable structures on paper significantly increases the conductivity, widens the adsorption range, and enhances the photoelectrochemical ability, which enables the higher sensitivity and flexibility compared with traditional rigid sensors. On the basis of this novel protocol, a miniaturized and portable origami device realizes the CEA determination with a low detection limit of 1.0 pg mL^-1 and a wide linear range from 0.002 to 200 ng mL^-1. Thanks to the good biocompatibility, the paper-based device provides a new avenue for the detection of CEA on the cell surface which is promising for portable diagnostics in early tumor warning.

Label-free impedimetric sensing platform for microRNA-21 based on ZrO2-reduced graphene oxide nanohybrids coupled with catalytic hairpin assembly amplification

Herein, a sensitive electrochemical impedance sensor was constructed based on ZrO2-reduced graphene oxide (RGO)-modified electrode coupled with the catalytic hairpin assembly signal amplification strategy. Electrochemical impedance spectroscopy (EIS) was used to detect microRNA (miRNA) using the change in electron transfer resistance (ΔR et) originated from nucleic acid hybridization on the electrode surface. MiRNA-21 was used as a model to verify this strategy. The results indicated that ΔR et exhibited a good linear relationship with the concentration of miRNA-21 in the range from 1.0 × 10-14 mol L-1 to 1.0 × 10-10 mol L-1 with a detection limit of 4.3 × 10-15 mol L-1 (S/N = 3). Additionally, this sensor exhibited good selectivity, and it could be applied to detect miRNA-21 in human serum samples and measure the expression levels of miRNA-21 in human breast cancer cell lines (MCF-7); thus, this sensor has great potential in cancer diagnosis.

Enzyme-catalyzed Ag Growth on Au Nanoparticle-assembled Structure for Highly Sensitive Colorimetric Immunoassay

We have developed a sensitive colorimetric immunoassay with broad dynamic range using enzyme-catalyzed Ag growth on gold nanoparticle (NP)-assembled silica (SiO2@Au@Ag). To reduce Ag+ ion content and promote Ag growth on the assembled Au NPs, alkaline phosphatase (AP)-based enzymatic amplification was incorporated, which considerably increased the colorimetric read-out. As a model study, sandwich enzyme-linked immunosorbent assay (ELISA) was used to quantify target IgG. The immune complexes capture the Ab-IgG-AP-labeled detection Ab and trigger the enzyme-catalyzed reaction to convert 2-phospho-L-ascorbic acid to ascorbic acid in the presence of the target IgG. Ascorbic acid reduced Ag+ to Ag, which formed Ag shells on the surface of SiO2@Au and enhanced the absorbance of the SiO2@Au@Ag solution. Plasmonic immunoassay showed a significant linear relationship between absorbance and the logarithm of IgG concentration in the range of ca. 7 × 10-13 M to 7 × 10-11 M. The detection limit was at 1.4 × 10-13 M, which is several hundred folds higher than that of any conventional colorimetric immunoassay. Thus, our novel approach of signal-amplification can be used for highly sensitive in vitro diagnostics and detection of target proteins with the naked eye without using any sophisticated instrument.

Highly sensitive visual detection of amantadine residues in poultry at the ppb level: A colorimetric immunoassay based on a Fenton reaction and gold nanoparticles aggregation

Colorimetric biosensors for the on-site visual detection of veterinary drug residues are required for food control in developing countries and other resource-constrained areas, where sophisticated instruments may not be available. In this study, we developed a highly sensitive immunoassay for amantadine residues in poultry. By introducing a novel signal generation strategy into an indirect competitive immunoassay, a highly sensitive assay for amantadine residues in chicken was achieved for naked eye readout at the part per billion (ppb) level. Signal amplification was achieved in the designed immunoassay by combining conventional indirect competitive enzyme-linked immunosorbent assay, Fenton reaction-regulated oxidation of cysteine, and gold nanoparticle aggregation. Therefore, the cascade reaction remarkably enhanced the assay sensitivity and led to a pronounced color change from red to dark purple in the solution, which could be easily distinguished with the naked eye even at approximately 1 μg kg^-1 in poultry muscle. Moreover, the color change can be quantitatively assayed with a classic high-throughput plate reader for contaminated poultry samples. The limit of detection (LOD) was 0.51 nM (0.095 ng mL^-1). The recovery rates for spiked chicken samples ranged from 78% to 84% with relative standard deviations <15%. Therefore, we propose that this immunoassay could be generally applicable for on-site detection in the field of food control.

A Study on Micropipetting Detection Technology of Automatic Enzyme Immunoassay Analyzer

In order to improve the accuracy and reliability of micropipetting, a method of micro-pipette detection and calibration combining the dynamic pressure monitoring in pipetting process and quantitative identification of pipette volume in image processing was proposed. Firstly, the normalized pressure model for the pipetting process was established with the kinematic model of the pipetting operation, and the pressure model is corrected by the experimental method. Through the pipetting process pressure and pressure of the first derivative of real-time monitoring, the use of segmentation of the double threshold method as pipetting fault evaluation criteria, and the pressure sensor data are processed by Kalman filtering, the accuracy of fault diagnosis is improved. When there is a fault, the pipette tip image is collected through the camera, extract the boundary of the liquid region by the background contrast method, and obtain the liquid volume in the tip according to the geometric characteristics of the pipette tip. The pipette deviation feedback to the automatic pipetting module and deviation correction is carried out. The titration test results show that the combination of the segmented pipetting kinematic model of the double threshold method of pressure monitoring, can effectively real-time judgment and classification of the pipette fault. The method of closed-loop adjustment of pipetting volume can effectively improve the accuracy and reliability of the pipetting system.