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Conventional plant protease detection always suffers from high background interference caused by the complex coloring metabolites in plant cells. In this study, a bio-modified magnetic beads-based strategy was developed for sensitive and quantitative detection of plant vacuolar processing enzyme (VPE) activity. Cleavage of the peptide substrate (ESENCRK-FITC) after asparagine residue by VPE resulted in the 2-cyano-6-amino-benzothiazole (CABT)-functionalized magnetic beads capture of the severed substrate CRK-FITC via a condensation reaction between CABT and cysteine (Cys). The catalytic activity was subsequently obtained by the confocal microscopy imaging and flow cytometry quantitative analysis. The sensor system integrated advantages of (i) the high efficient enrichment and separation capabilities of magnetic beads and (ii) the catalyst-free properties of the CABT-Cys condensation reaction. It exhibited a linear relationship between the fluorescence signal and the concentration of severed substrate in the range of 10–600 pM. The practical results showed that, compared with normal growth conditions, VPE activity was increased by 2.7-fold (307.2±25.3 μM min −1 g −1 ) upon cadmium toxicity stress. This platform effectively overcame the coloring metabolites-caused background interference, showing fine applicability for the detection of VPE activity in real samples. The strategy offers great sensitivity and may be further extended to other protease activity detection. [ABSTRACT FROM AUTHOR]

Abstract: The mixture of graphene oxide (GO) and aptamer labeled fluorophore is widely used in developing fluorescent sensors for the analysis of biomolecules, according to the light signal ‘off–on’ procedure. Moreover, the laser-induced fluorescence-coupled affinity probe capillary electrophoresis (APCE) technique has been broadly applied for the separation of micromolecules. Here, a strategy is proposed for analysis of content of carcino-embryonic antigen (CEA) based on the combination of GO and quantum dots labeling aptamer (QD–aptamer) by capillary electrophoresis (CE). The method has three advantages: (i) combined with CE, only few samples are required and efficiency of separation is high, (ii) fluorescent detection can be carried out after separation of GO and fluorescence probe combined with targets by CE, while fluorescence detection sensitivity had been greatly improved, and (iii) the issues of APCE, including the effect of excess fluorescence probe and maximizing separation between analytes, could be solved by introducing GO. It has been proved that QD–aptamer–CEA complex can completely dissociate from GO. Results show that the fluorescence intensity has a linear relationship with the concentration of CEA in the range from 0.257 to 12.9ng/mL, and the limit of detection is approximately 5pg/mL (S/N=3). The proposed method with high specificity has been applied for the accurate analysis of content of CEA in patient׳s serum. [Copyright &y& Elsevier]

Abstract: A new sandwich-type electrochemical immunosensor based on nanosilver-doped bovine serum albumin microspheres (Ag@BSA) with a high ratio of horseradish peroxidase (HRP) and detection antibody was developed for quantitative monitoring of biomarkers (carcinoembryonic antigen, CEA, used in this case) by coupling enzymatic biocatalytic precipitation with tyramine signal amplification strategy on capture antibody-modified glassy carbon electrode. Two immunosensing protocols (with and without tyramine signal amplification) were also investigated for the detection of CEA and improved analytical features were acquired with tyramine signal amplification strategy. With the labeling method, the performance and factors influencing the electrochemical immunoassay were studied and evaluated in detail. Under the optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range of 0.005–80ngmL−1 toward CEA standards with a low detection limit of 5.0pgmL−1. Intra- and inter-assay coefficients of variation were below 11%. No significant differences at the 0.05 significance level were encountered in the analysis of 6 clinical serum specimens and 6 spiked new-born cattle serum samples between the electrochemical immunoassay and the commercialized electrochemiluminescent immunoassay method for the detection of CEA. [Copyright &y& Elsevier]

Abstract: Two nanostructures including carbon nanospheres-graphene hybrid nanosheets (CNS-GNS) and hollow platinum nanospheres (HPtNS) were first synthesized by using direct electrolytic reduction and wet chemistry methods, respectively. Thereafter, a specific sandwich-type electrochemical immunoassay was designed for determination of carcinoembryonic antigen (CEA) by using HPtNS-labeled horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA) as molecular tags and anti-CEA-assembled CNS-GPS as sensing probes. Compared with pure graphene nanosheets, the presence of carbon nanospheres on the graphene increased the surface coverage of the substrate, and enhanced the immobilized amount of primary antibodies. Several labeling protocols, such as HRP-anti-CEA, solid platinum nanoparticle-labeled HRP-anti-CEA, and hollow platinum nanospheres-labeled HRP-anti-CEA, were investigated for determination of CEA and improved analytical features were obtained with hollow platinum nanosphere labeling. With the HPtNS labeling method, the effects of incubation time and pH on the current responses of the immunosensors were also studied. The strong attachment of biomolecules to the CNS-GPS and HPtNS resulted in a good repeatability and intermediate precision down to 10.2%. The dynamic concentration range spanned from 0.001ngmL−1 to 100ngmL−1 CEA with a detection limit of 1.0pgmL−1 at the 3S blank level. No significant differences at the 0.05 significance level were encountered in the analysis of 10 clinical serum samples between the developed immunoassay and the commercially available electrochemiluminescent method for determination of CEA. [Copyright &y& Elsevier]

The expression level of glucose transporter 1 (GLUT-1) is highly correlated with tumor malignancy, making it a promising therapeutic target for cancer treatment. The detection of GLUT-1 expression level is significant for cancer discovery and valuating the efficacy of drug treatments. However, current methods for GLUT-1 detection primarily rely on traditional techniques. Therefore, the development of anon-destructive in vivo monitoring system would be invaluable for assessing GLUT-1 expression and tumor responses to various drugs. In this study, an electrochemical platform for detection of GLUT-1 on living cells was established using reduced graphene oxide-multi-wall carbon nanotube composite (rGO-MWCNT) as a conductive coating and toluidine blue O (TBO)-graphene-gold nanoparticle-GLUT-1 antibody as the electrochemical probe. The sensor demonstrated excellent performance in detecting GLUT-1 on cells with a linear range of 10 - 105 cells/mL, good stability and selectivity. The sensor successfully detected GLUT-1 expressions in multiple tumor cell types, including those treated with siRNA or drugs, and the results were consistent with those obtained from traditional methods such as flow cytometry, western blotting, and immunofluorescence. The sensor is promising in evaluating the malignant level of tumor cells, distinguishing glucose uptake pathways in tumor cells, reducing medical costs, and facilitating the translation of electrochemical sensing technology to the clinical settings. • Our biosensor specifically recognizes GLUT-1 protein expressed on the surface of living cancer cells. • The electrical signal produced by the biosensor exhibits changes corresponding to changes in cell number. • Our biosensor is quick and easy to implement and paves the way for in situ evaluation of GLUT-1 and related drug. • The design features of the sensor allow simultaneous detection of multiple cells and clinical samples. [ABSTRACT FROM AUTHOR]

Nucleic acid (NA) is a widely-used biomarker for viruses. Accurate quantification of NA can provide a reliable basis for point-of-care diagnosis and treatment. Here, we propose a tilted fiber Bragg grating (TFBG)-based plasmonic fiber-optic spectral comb for fast response and ultralow limit NA detection. The TFBG is coated with a gold film which enables excitation of surface plasmon resonance (SPR), and single-stranded probe NAs with known base sequences are assembled on the gold film. To enhance sensitivity of refractive index (RI) for sensing a chosen combination of probe and target NAs around the TFBG surface, gold nanoparticles (AuNPs) are bonded to the target NA molecules as "RI-labels". The NA combination-induced aggregation of AuNPs induces significant spectral responses in the TFBG that would be below the detection threshold for the NAs in the absence of the AuNPs. The proposed TFBG-SPR NA sensor shows a fast response time of 30 s and an ultra-wide NA detection range from 1 × 10−18 mol/L to 1 × 10−7 mol/L. In the NA concentration range of 1 × 10−12 mol/L (1 pM) to 105 pM, an ultra-high sensitivity of 1.534 dB/lg(pM) is obtained. The sensor achieves an ultra-low limit of detection down to 1.0 × 10−18 mol/L (1 aM), which is more than an order of magnitude lower than the previous reports. The proposed sensor not only shows potentials in practical applications of NA detection, but also provides a new way for TFBG-SPR biochemical sensors to achieve higher RI sensitivity. [ABSTRACT FROM AUTHOR]

The spread of SARS-CoV-2 virus in the ongoing global pandemic has led to infections of millions of people and losses of many lives. The rapid, accurate and convenient SARS-CoV-2 virus detection is crucial for controlling and stopping the pandemic. Diagnosis of patients in the early stage infection are so far limited to viral nucleic acid or antigen detection in human nasopharyngeal swab or saliva samples. Here we developed a method for rapid and direct optical measurement of SARS-CoV-2 virus particles in one step nearly without any sample preparation using a spike protein specific nanoplasmonic resonance sensor. As low as 370 vp/mL were detected in one step within 15 min and the virus concentration can be quantified linearly in the range of 0 to 107 vp/mL. Measurements shown on both generic microplate reader and a handheld smartphone connected device suggest that our low-cost and rapid detection method may be adopted quickly under both regular clinical environment and resource-limited settings. Image 1 • 15min one step SARS-CoV-2 viral particles detection. • No sample processing and low-cost equipment and biosensor chip. • Sensitive for asymptomatic carriers diagnosis potentially. [ABSTRACT FROM AUTHOR]

We report a triplex signal amplification strategy for sensitive biosensing of cancer biomarker by taking advantage of hairpin-shaped oligonucleotide-functionalized gold nanorods (HO-GNRs), graphene and the avidin-biotin reation. The strategy expands electrochemical detection of carcinoembryonic antigen (CEA) by using an aptamer as biosensor's recognition element and HO-GNRs as signal enhancer. To construct this biosensor, the GNR was used as a carrier of horseradish peroxidase (HRP) and HO aptamer with a biotin at the 3′-end and a thiol at the 5′-end, which amplified the electrochemical response because of a large molar ratio of HRP to HO. In the presence of target CEA, the binding reactions of CEA with the loop portions of the HOs caused HOs’ loop-stem structure opened and exposed the biotins, and then HRP-GNRs-HO conjugates were captured on graphene and streptavidin modified electrodes via the reaction between the exposed biotins and preimmobilized streptavidins. The accumulation of HRP effectively catalyzed the hydrogen peroxide-mediated oxidation of o -phenylenediamine to generate an electrochemical reduction current for CEA detection. Under optimal conditions, the electrochemical biosensor exhibited a wide dynamic range of 5 pg mL −1 and 50 ng mL −1 toward CEA standards with a low detection limit of 1.5 pg mL −1 (signal-to-noise ratio of 3). The proposed biosensor accurately detected CEA concentration in 8 human serum samples from patients with lung diseases, showing excellent correlations with standard chemiluminescence immunoassay. Furthermore, these results of target DNA detection made it abundantly clear that the proposed strategy can also be extended for detection of other relative biomarkers using different functional DNA structures, which shows great prospects in single-nucleotide polymorphisms analysis, biomedical sensing and application for accurate clinical diseases diagnostic. [ABSTRACT FROM AUTHOR]

Although immunotherapy is now well established in cancer management, not every patient responds. Existing methods for assessing tumor immunotherapy responses, such as immunohistochemistry of the immune checkpoint protein programmed death ligand-1 (PD-L1), require destructive tissue analysis; furthermore, real-time in vivo monitoring would be beneficial for assessing tumor responses. Here we establish an electrochemical biosensor which was developed based on molybdenum disulfide (MoS 2) and multi-wall carbon nanotubes (MWCNTs) used to modify the electrode and PD-L1 antibody-quantum dot (QD) conjugate as a dual optical and electrochemical label. The compositions, electrochemical performance, specificity of nanocomposite and probe were characterized. Paving the way for clinical application, the prepared biosensor detects differences in PD-L1 levels in diverse tumor cell types, tumors derived from mice or cancer patients, and it is reproducible and selective in both phosphate-buffered saline and serum. This study demonstrates that electrochemical sensing is a desirable technology for the in-situ and dynamic determination of biomarkers on the cellular level of for the assessment of tumor immunotherapy. [ABSTRACT FROM AUTHOR]

It is tremendously desirable for the timely and effective detection of cancer to facilitate the ultra-highly sensitive monitoring of tumor marker in clinical serum sample. In this study, an electromagnetic and chemical synergistically enabled recyclable immunoassay based on surface-enhanced Raman scattering (SERS) was proposed by realizing the anisotropic growth of sea-urchin-like gold nanoflowers (Au NFs) on two-dimensional red phosphorus (RP) nanoplates. Besides the achieved enhancement factor as high as 2.24 × 106, it was found that the photocatalytic and SERS activities were kept at a high level for the hybrid substrate of RP/Au NFs throughout 7 cycles of immunoassay. In combination with a non-metallic immunoprobe, the limit of detection was drove to 7.41 × 10−5 IU·mL−1 for cancer antigen 19–9. The comparative experiments of nonspecific monitoring verified the promising selectivity of this strategy. Considering the intriguing features of high sensitivity, recyclability, and specificity, the proposed multifunctional RP/Au NFs exhibited its superior role in the early detection of cancer and can be adapted for point-of-care diagnosis. ► A symmetric Au nanoflowers have been successfully decorated onto the RP nanosheet. ► Abundant bright "hot spots" around decorated sea-urchin-like Au nanoflowers were confirmed. ► A recyclable immunoassay strategy has been demonstrated by RP/Au NFs hybrid substrate. [ABSTRACT FROM AUTHOR]

Abstract: Microbial fuel cells (MFCs) are promising for harnessing bioenergy from various organic wastes. However, low electricity power output (EPT) is one of the major bottlenecks in the practical application of MFCs. In this study, EPT improvement by cofactor manipulation was explored in the Pseudomonas aeruginosa-inoculated MFCs. By overexpression of nadE (NAD synthetase gene), the availability of the intracellular cofactor pool (NAD(H/+)) significantly increased, and delivered approximately three times higher power output than the original strain (increased from 10.86μW/cm2 to 40.13μW/cm2). The nadE overexpression strain showed about a onefold decrease in charge transfer resistance and higher electrochemical activity than the original strain, which should underlie the power output improvement. Furthermore, cyclic voltammetry, HPLC, and LC–MS analysis showed that the concentration of the electron shuttle (pyocyanin) increased approximately 1.5 fold upon nadE overexpression, which was responsible for the enhanced electrochemical activity. Thus, the results substantiated that the manipulation of intracellular cofactor could be an efficient approach to improve the EPT of MFCs, and implied metabolic engineering is of great potential for EPT improvement. [Copyright &y& Elsevier]

Recently, nonmetallic substrates have stimulated great interest in surface-enhanced Raman scattering (SERS)-based immunoassay owing to their good uniformity, stability, and biocompatibility. In this context, a novel nonmetallic SERS-based immunoassay mediated by two-dimensional molybdenum disulfide (MoS 2) was delivered for the sensitive and specific monitoring of carbohydrate antigen 19–9 (CA19-9). The effective enrichment of molecules on the large active surfaces of MoS 2 as well as potential 532-nm laser-induced charge transfer resonances between them engendered desirable enhancement factor values at the level of 105. Intriguingly, a sandwich immunocomplex combined MoS 2 nanoflower and nanosheet exhibited not only a wide linear range from 5 × 10−4 to 1 × 102 IU·mL−1 but also a limit of detection as low as 3.43 × 10−4 IU·mL−1 towards CA19-9. More meaningful, the analytical result for clinical patient serum sample was basically compared with the conventional chemiluminescent immunoassay. Such a novel nonmetallic SERS-based immunosensor with desirable biocompatibility and sensitivity is promising for clinical diagnosis. • A novel nonmetallic SERS-based immunoassay mediated by two-dimensional molybdenum disulfide (MoS 2) was developed. • Potential 532-nm laser-induced CT resonances between MoS 2 and R6G engendered a fascinating EF value of 105. • The sensitive and specific monitoring of carbohydrate antigen 19–9 in human serum has been achieved by the nonmetallic SERS-based immunoassay. [ABSTRACT FROM AUTHOR]

Abstract: Silicon-on-insulator (SOI) wafer is one of the most appealing platforms for optical integrated circuit with the potential to realize high performance Ultra Large Scale Integration (ULSI) and device miniaturization. In this work, based on simulations to obtain appropriate optical properties of a porous silicon microcavity (PSM), we successfully fabricated a highly efficient PSM on SOI wafer by electrochemical etching for DNA detection at optical wavelength 1555.0nm. The narrow resonance peak with a full width at half maximum about 26.0nm in the reflectance spectrum gives a high Q factor which causes high sensitivity for sensing performance. The sensitivity of this sensor is investigated through 19-base pair DNA hybridization in the PSM by surface modification using a standard cross link chemistry method. The red shift of the reflectance spectra shows a good linear relationship with complementary DNA concentration, ranging from 0.625 to 12.500μM, and the detection limit is 43.9nM. This optical PSM on SOI is highly sensitive, fast responsive, easy to fabricate and low-costly, that will broadly benefit to develop a new optical label-free biosensor on SOI wafer and has a great potential for biochips based on integrated optical devices. [Copyright &y& Elsevier]

Abstract: A label-free oligonucleotide-based luminescent switch-on assay has been developed for the selective detection of sub-nanomolar Pb2+ ions in aqueous solution and real water samples. An iridium(III) complex was employed as a G-quadruplex specific luminescent probe and a guanine rich DNA (PS2.M, 5′-GTG3TAG3CG3T2G2-3′) was employed as recognition unit for Pb2+ ions. The PS2.M exists in a single-stranded conformation in the absence of Pb2+ ions, and the weak binding of the iridium(III) probe to ssDNA results in a weak luminescence signal. Upon binding to Pb2+ ions, the single-stranded DNA sequence (PS2.M) is induced into a G-quadruplex conformation, which greatly enhances the luminescence emission of the iridium(III) probe. The assay can detect Pb2+ ions in aqueous media with a limit of detection of 600pM. It also exhibits good selectivity for Pb2+ ions over other heavy metal ions. Furthermore, the application of the assay for the detection of Pb2+ ions in spiked river water samples has been demonstrated. [Copyright &y& Elsevier]

Abstract: A facile and feasible magneto-controlled immunosensing platform was designed for sensitive electrochemical immunoassay of brevetoxin B (BTX-2) in seafood by using guanine-assembled graphene nanoribbons (GGNRs) as molecular tags on a home-made magnetic carbon paste electrode. Initially, monoclonal mouse anti-BTX-2 antibodies were covalently immobilized on the surface of magnetic beads, which were used as the immunosensing probes for the capture of BTX-2. The recognition elements were prepared by chemical modification of bovine serum albumin-BTX-2 conjugates (BTX-2-BSA) with the GGNRs. Based on a competitive-type immunoassay format, the formed magnetic immunocomplex was integrated on the electrode with an external magnet, followed by determination in pH 6.5 phosphate-buffered solution containing 2μM Ru(bpy)3Cl2. Under optimal conditions, the electrochemical signals decreased with the increasing BTX-2 concentrations in the sample. The dynamic concentration range spanned from 1.0pgmL−1 to 10ngmL−1 with a detection limit of 1.0pgmL−1 BTX-2. Inter- and intra-batch assay precisions were substantially improved by resorting to the GGNR manifold. The method featured unbiased identification of negative (blank) and positive samples. No significant differences at the 95% confidence level were encountered in the analysis of 12 spiked samples including S. constricta, M. senhousia and T. granosa between the electrochemical immunoassay and commercially available enzyme-linked immunosorbent assay (ELISA) for determination of BTX-2. [Copyright &y& Elsevier]

A critical barrier for the successful development of fiber sensors for bio-chemical processes is their limitedly improved sensitivity, restricted by the sensor structural design. To solve this, in this paper, a novel concept was proposed using functionalised modified magnetic microspheres (MMSs) to "amplify" the effect of target bio-chemical analytes to significantly improve the fiber sensor's sensitivity, which has been demonstrated using human chorionic gonadotropin (hCG) as an example. Two types of antibody hCG, ( β and α , both can specifically bind with hCG), were adhered on the surface of fibre sensor and MMSs respectively. Both hCG and MMSs will be specifically captured by the fibre sensor, where MMSs act as an "amplifier" to improve the sensor sensitivity. Experimentally immunomagnetic detection limit of 0.0001 mIU/mL has been achieved, which is the highest reported so far. This newly developed methodology opens a new direction for sensitivity improvement and could be further explored to applications require ultrahigh sensitivity detections such as earlier medical diagnostics. • Use surface modified magnetic microspheres (MMSs) to "amplify" the signal of target analyte. • Provide "additional" sensitivity improvement for the fabricated sensor. • Demonstrated limit of detection of human chorionic gonadotropin as low as 0.0001 mIU/mL, the best value reported so far. • The concept will be pivotal for applications require ultra-high sensitivity detection such as early medical diagnostics.. [ABSTRACT FROM AUTHOR]