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Three-dimensional (3D) printed electrochemical devices are increasingly used in point-of-need and point-of-care testing. They show several advantages such as simple fabrication, low cost, fast response, and excellent selectivity and sensitivity in small sample volumes. However, there are only a few examples of analytical devices combining 3D-printed electrodes with electrochemiluminescence (ECL) detection, an electrochemical detection principle widely employed in clinical chemistry analysis. Herein, a portable, 3D-printed miniaturized ECL biosensor for glucose detection has been developed, based on the luminol/H2O2 ECL system and employing a two-electrode configuration with carbon black-doped polylactic acid (PLA) electrodes. The ECL emission is obtained by means of a 1.5V AA alkaline battery and detected using a smartphone camera, thus providing easy portability of the analytical platform. The ECL system was successfully applied for sensing H2O2 and, upon coupling the luminol/H2O2 system with the enzyme glucose oxidase, for glucose detection. The incorporation of luminol and glucose oxidase in an agarose hydrogel matrix allowed to produce ECL devices preloaded with the reagents required for the assay, so that the analysis only required sample addition. The ECL biosensor showed an excellent ability to detect glucose up to 5 mmol L-1, with a limit of detection of 60 mu mol L-1. The biosensor was also used to analyse real samples (i.e., glucose saline solutions and artificial serum samples) with satisfactory results, thus suggesting its suitability for point-of-care analysis. Coupling with other oxidases could further extend the applicability of this analytical platform.

MiRNAs hold great potential as biomarkers for the early detection and monitoring of diseases based on their differential expression profiles. Therefore, the sensitive, specific and accurate detection of miRNAs represents an emerging new tool to improve diagnosis and treatment of several diseases, cancer in particular. DNA origami-based miRNA detection is particularly advantageous as it allows to incorporate multiple attachment sites to capture different target miRNAs at the nanoscale. In this work, we present a DNA origami nanoarray system providing distance-dependent recognition of miRNAs by applying super-resolution microscopy technique; DNA-PAINT (point accumulation for imaging in nanoscale topography). The sensor can detect up to 4 miRNAs either separately or in combination based on the relative distance to the boundary markers on the structure using a single imager strand. The detection is highly sensitive, with a limit of detection down to the low femtomolar range (11 fM - 388 fM) and has a large dynamic range up to 10 nM without need for amplification. Moreover, our detection system can discriminate single base mismatches with low false positive rates. Using our strategy, we demonstrate the detection of endogenous miRNAs from cell extracts of cancer cell lines and plasma from breast cancer patients. Overall, we developed an ultrasensitive and amplification-free, DNA-PAINT imaging-based miRNA detection method using DNA origami nanoarray system for the detection of breast-cancer associated miRNAs which potentially provides a sensitive and accurate alternative to the current multiplexed diagnostic technologies.

With the increased demand for beef in emerging markets, the development of quality-control diagnostics that are fast, cheap and easy to handle is essential. Especially where beef must be free from pork residues, due to religious, cultural or allergic reasons, the availability of such diagnostic tools is crucial. In this work, we report a label-free impedimetric genosensor for the sensitive detection of pork residues in meat, by leveraging the biosensing capabilities of graphene acid - a densely and selectively functionalized graphene derivative. A single stranded DNA probe, specific for the pork mitochondrial genome, was immobilized onto carbon screen-printed electrodes modified with graphene acid. It was demonstrated that graphene acid improved the charge transport properties of the electrode, following a simple and rapid electrode modification and detection protocol. Using non-faradaic electrochemical impedance spectroscopy, which does not require any electrochemical indicators or redox pairs, the detection of pork residues in beef was achieved in less than 45 min (including sample preparation), with a limit of detection of 9% w/w pork content in beef samples. Importantly, the sample did not need to be purified or amplified, and the biosensor retained its performance properties unchanged for at least 4 weeks. This set of features places the present pork DNA sensor among the most attractive for further development and commercialization. Furthermore, it paves the way for the development of sensitive and selective point-of-need sensing devices for label-free, fast, simple and reliable monitoring of meat purity., We acknowledge funding from the European Union Horizon2020 Programme under Grant No. 881603 (Graphene Flagship Core 3). This article reflects only the author's view, and the European Commission is not responsible for any use that may be made of the information it contains. ICN2 is funded by the CERCA programme, Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). J. M. R. Flauzino is grateful for the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior scholarship (CAPES-PRINT, Brazil, Grant number: 88887.371591/2019–00). D. Panáček acknowledges the Internal Student Grant Agency of the Palacký University in Olomouc, (IGA_PrF_2021_031). A. G. Brito-Madurro acknowledges the funding from Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq (310782/2018–0). J. M. Madurro acknowledges the funding from Fundação de Amparo à Pesquisa do Estado de Minas Gerais – FAPEMIG (CEX-APQ-02902-17) and Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (311737/2018–8). A. Bakandritsos acknowledges the funding from the Czech Science Foundation, (project GA CR – EXPRO, 19–27454X). M. Otyepka acknowledges the ERC grand 2D-CHEM (No 683024 from H202). The work was supported also by the ERDF/ESF project “Nano4Future” (No.CZ.02.1.01/0.0/0.0/16_019/0000754).

International audience; One of the main challenges in terms of public health concerns the prevention of bacterial contamination using rapid, highly sensitive and specific detection techniques. The development of highly sensitive bacterial sensors for Escherichia coli detection based on networks of silicon nanowires has been carried out in this work. The interest of these nano-objects takes advantage in a large contact surface allowing potentially important interactions with bacteria. Their presence induces a change in electrical interaction through the silicon nanowires array and is the basis for the development of silicon nanowires based electrical resistances acting as bacteria sensors. High specificity of these sensors is ensured by chemical functionalization of the nanowires allowing the binding of specific antibodies targeting the lipopolysaccharide (anti-LPS) of E. coli, but not S. aureus. The sensor displays a sensitivity of 83 μA per decade of CFU/mL due to the nanometric dimensions of the nanowires. The electrical measurements ensure the detection of various E. coli concentrations down to 102 CFU/mL. This SiNW biosensor device demonstrated its potential as an alternative tool for real-time bacterial detection as miniaturizable and low-cost integrated electronic sensor compatible with the classical silicon technology.

On global scale, the current situation of pandemic is symptomatic of increased incidences of contagious diseases caused by pathogens. The faster spread of these diseases, in a moderately short timeframe, is threatening the overall population wellbeing and conceivably the economy. The inadequacy of conventional diagnostic tools in terms of time consuming and complex laboratory-based diagnosis process is a major challenge to medical care. In present era, the development of point-of-care testing (POCT) is in demand for fast detection of infectious diseases along with “on-site” results that are helpful in timely and early action for better treatment. In addition, POCT devices also play a crucial role in preventing the transmission of infectious diseases by offering real-time testing and lab quality microbial diagnosis within minutes. Timely diagnosis and further treatment optimization facilitate the containment of outbreaks of infectious diseases. Presently, efforts are being made to support such POCT by the technological development in the field of internet of medical things (IoMT). The IoMT offers wireless-based operation and connectivity of POCT devices with health expert and medical centre. In this review, the recently developed POC diagnostics integrated or future possibilities of integration with IoMT are discussed with focus on emerging and re-emerging infectious diseases like malaria, dengue fever, influenza A (H1N1), human papilloma virus (HPV), Ebola virus disease (EVD), Zika virus (ZIKV), and coronavirus (COVID-19). The IoMT-assisted POCT systems are capable enough to fill the gap between bioinformatics generation, big rapid analytics, and clinical validation. An optimized IoMT-assisted POCT will be useful in understanding the diseases progression, treatment decision, and evaluation of efficacy of prescribed therapy.

Despite the fact that cancer research has experienced important advances and remarkable improvement in the curing processes during the last decades, this disease still occupies a leading position among the causes of death worldwide. It has been demonstrated that there is an interconnection between the overexpression of interleukin-6 cytokine and the tumor growth, metastasis, and therapeutic resistance in several types of malignancies. Herein, a highly sensitive and selective aptasensor for quantitative detection of interleukin-6 was developed by using a glassy carbon electrode modified with p-aminobenzoic acid, p-aminothiophenol and gold nanoparticles. A thio-terminated aptamer specific for interleukin-6 was immobilized on the surface of the modified electrode via the formation of gold-sulfur bonds. This DNA oligonucleotide was then used as a detection probe to capture the target protein at the biosensor surface allowing label-free detection by electrochemical impedance spectroscopy. The developed aptasensor showed a good linear response from 5 pgmL−1 to 100 ngmL−1 with a detection limit of 1.6 pgmL−1, within the range of physiological concentration of the protein. The biosensor exhibited high selectivity and has been successfully used to detect interleukin-6 in blood samples collected from patients suffering of colorectal cancer, with excellent recoveries after the addition of known amount of the target protein.

MicroRNAs (miRNAs) are regarded as a large variety of cancer-related biomarkers, and they have attracted wide attentions in recent years. In this work, a novel label-free strategy for the ultrasensitive detection of miRNA-182 (a typical biomarker for lung cancer) based on MoS2/Ti3C2 nanohybrids was suggested. Firstly, modified glassy carbon electrode (GCE) with massive active sites and good electronic conductivity was prepared for biosensing. Then, based on this platform a descent signal in differential pulse voltammetry (DPV) peak current could be observed with the addition of probe RNA with negative charge. Thereafter, with the hybridization of target miRNA-182 with immobilized probe RNA and the swelling-induced breakage of Au–S bonds between RNA and the electrode surface, the characteristic DPV signals increase were found. In particular, this biosensing platform for special miRNAs possessed a good linear detection window in a range from 1 fM to 0.1 nM with a detection limit of 0.43 fM.

How to in situ detect intracellular telomerase activity with high sensitivity still faces many challenges. This paper constructs a new fluorescence biosensing platform for the sensitive detection of intracellular telomerase activity via the combination of nanoflare and hybridization chain reaction (HCR)-based signal amplification on a single patchy gold/carbon nanosphere (PG/CNS), which has two or more distinct parts and allows hybridized-DNA (HS-DNA/Primer-DNA/Flare-DNA) and H1/H2-DNA (a pair of cross complementary DNA hairpins) to bind onto their surfaces via Au–S bond and electrostatic interaction, respectively. In the presence of telomerase, Primer-DNA (telomerase primer) extends at its 3′ end to produce a telomeric repeated sequence, resulting in the release of Flare-DNA followed by the recovery of the fluorescence. Subsequently, the released Flare-DNA further initiates cross hybridization of H1 and H2 DNA from mimic-HCR system to amplify the fluorescence signal. The in vivo confocal microscopy studies demonstrate that resulting sensor can enter into the cancer cells such as A549 cells, and lead to the increase in luminescence, which is stronger than the sensor without the HCR-based signal amplification system. A linear relationship between the fluorescence intensity and the amount of A549 cells is observed, and the limit of detection of the sensor reaches about 280 A549 cells.

We report on a wearable tear bioelectronic platform, integrating a microfluidic electrochemical detector into an eyeglasses nose-bridge pad, for non-invasive monitoring of key tear biomarkers. The alcohol-oxidase (AOx) biosensing fluidic system allowed real-time tear collection and direct alcohol measurements in stimulated tears, leading to the first wearable platform for tear alcohol monitoring. Placed outside the eye region this fully wearable tear-sensing platform addresses drawbacks of sensor systems involving direct contact with the eye as the contact lenses platform. Integrating the wireless electronic circuitry into the eyeglasses frame thus yielded a fully portable, convenient-to-use fashionable sensing device. The tear alcohol sensing concept was demonstrated for monitoring of alcohol intake in human subjects over multiple drinking courses, displaying good correlation to parallel BAC measurements. We also demonstrate for the first time the ability to monitor tear glucose outside the eye and the utility of wearable devices for monitoring vitamin nutrients in connection to enzymatic flow detector and rapid voltammetric scanning, respectively. These developments pave the way to build an effective eyeglasses system capable of chemical tear analysis.

A suspended carbon nanotube (SCNT)-based field effective transistor (SCNT-FET), which was fabricated by utilizing the surface tension of liquid silver to suspend a CNT between two Pd electrodes, was proposed for the detection of DNA hybridization. Benefits from the separation between the CNT and the substrates could be observed; namely, the conductivity of a SCNT-FET was much higher (two orders of magnitude) than that of a FET based on an unsuspended CNT and about 50% sensing surface of CNT was freed from substrate. The Slater-Koster tight-binding method was adopted for geometry optimization and transport property calculation of the SCNT bound with DNA. The result showed that the conductance (G = 1/R) of the SCNT decreased in order with the binding of single-stranded DNA (SSDNA, probe DNA) and double-stranded DNA (DSDNA) and that the ability of DSDNA to weaken the conductivity of the SCNT was several times higher than that of SSDNA. SEM and Raman spectroscopy were used to demonstrate that DNA could be bound successfully onto the SCNT using a 1-pyrenebutanoic acid succinimidyl ester (PBASE) as a linkage. Ultra-high sensitivity detection of DNA [with a limit of detection (LOD) as low as 10 aM] was obtained using such an SCNT-FET, which showed a lower value than that of a previously reported FET DNA biosensor whose sensing materials were in direct contact with the substrate.

Oxygen defect-engineered is an important strategy to improve the photoelectric activity of materials. Herein, a facile one-pot solvothermal method was utilized to synthesize visible light-responsive photoactive Bi2MoO6 nanoparticles anchored boron and nitrogen co-doped graphene (BNG) nanosheets nanocomposites with oxygen vacancy. The incorporation of BNG nanosheets increased the oxygen vacancies amounts on Bi2MoO6 remarkably, and the presences of oxygen vacancies can be beneficial to broaden the absorption range. The absorption edge of Bi2MoO6/BNG was widened from 500 nm to 550 nm compared to Bi2MoO6, and the charge transfer was accelerated to improve the photoactive of Bi2MoO6/BNG. Under visible light illumination, the photoelectrochemical (PEC) response of the as-prepared Bi2MoO6/BNG was 11.6-fold, 6.7-fold, 3.1-fold and 2.4-fold higher than that of pristine Bi2MoO6, Bi2MoO6/graphene, Bi2MoO6/nitrogen doped graphene and Bi2MoO6/boron doped graphene. Using Bi2MoO6/BNG nanocomposites with the superior PEC performance as photoactive materials in combination with specifically recognized lincomycin (LIN) aptamer, a highly efficient PEC aptasensor was successfully constructed for sensitive analysis of LIN. Under optimal conditions, the proposed PEC aptasensor exhibited excellent analytical performance for LIN with a wide linear response of 1 × 10−11 to 1 × 10−6 mol L−1 along with a low detection limit of 3.7 × 10−12 mol L−1 (defined as S/N = 3). The as-prepared Bi2MoO6/BNG nanocomposites exhibit excellent visible light response and PEC performance, indicating its potential applications in PEC biosensor.

This work utilized ultrathin metal-organic layer (MOL) to immobilize luminophores for effectively shortening the ion/electron-transport distance and relieving the diffusional constraints of ion/electron, which greatly enhanced the ECL efficiency and intensity. Moreover, the MOL's immobilization amount of luminophores should be higher than these of bulk MOFs because MOLs possess more accessible postmodification sites for the luminophores with minimal diffusion barriers. As expected, our proof-of-concept experiment indicated that the Hf-MOL's loading number of Ru(bpy)2(mcpbpy)2+ was about 1.74 times that of a 3D mesoporous MOF (PCN-777), and the ECL efficiency and intensity of PEI@Ru-Hf-MOL were around 1.27 times and 14.5 times those of PEI@Ru-PCN-777, respectively. In view of these merits, this work utilized the prepared PEI@Ru-Hf-MOL as a highly efficient sensing platform for simple, rapid and sensitive detection of mucin 1, which exhibited a broad linearity from 1 fg/mL to 10 ng/mL and a low detection limit of 0.48 fg/mL. This work provided a practicable strategy to develop high-performance ECL materials, and therefore opened up a new avenue to design ultrasensitive ECL biosensors, which expanded the application potential of MOLs in ECL assays.

This review article presents an overview of recent work on electrochemical biosensors developed using microfabrication processes, particularly sensors used to achieve sensitive and specific detection of DNA sequences. Such devices are important as they lend themselves to miniaturisation, reproducible mass-manufacture, and integration with other previously existing technologies and production methods. The review describes the current state of these biosensors, novel methods used to produce them or enhance their sensing properties, and pathways to deployment of a complete point-of-care biosensing system in a clinical setting.

The detection of Cu2+ ion, one of the metal ions substantial in cerebral physiology, is critical in studying brain activities and understanding brain functions. However, repetitive measurements of Cu2+ in the progress of physiological and pathological events is still challenging, because lack of the platform for repetitive on-line detection-regeneration cycle. Herein we report the design of a regenerated electrochemical biosensor combined with the in vivo microdialysis system. In this biosensor, hyperbranched polyethyleneimine (hPEI) acts as a regenerated recognition unit for Cu2+. Just by a simple rinse of ethylenediaminetetraacetic acid (EDTA) disodium salt, the Cu2+ and Cu+ ions on the biosensor interface were chelated with EDTA disodium salt, thus achieving the regeneration of the biosensor. In addition, 6-(ferrocenyl)hexanethiol (FcHT) serves as the inner reference moiety to elevate the sensing accuracy over regeneration cycles. As a result, this ratiometric electrochemical biosensor not only revealed high sensitivity and selectivity, but also exhibited excellent stability during multiple regeneration processing. This biosensor was capable of determining Cu2+ with a linear range between 0.05 and 12 μM and low detection limit (LOD) of 13 nM. Then, the platform has been successfully applied in repetitive Cu2+ analysis in rat brain under global cerebral ischemia/reperfusion events. The combination of results from 7 rats indicates global cerebral ischemia caused an obvious increase of the Cu2+ level, while reperfusion brought this level back to normal.

DNA methylation is catalyzed by DNA methyltransferase (MTase) and concerned with many biological processes including pathogenesis of various human diseases. The monitoring of MTase activity is thus of great significance in disease diagnosis and drug screening. Herein, we developed a facile way to synthesize biocompatible invertase enzyme modified metal-organic framework (Invertase/MOF) materials, and explored its application in constructing a dual-response Dam MTase sensor for the first time. By using them as signal probes, in which high density of metal sites could be electrochemically detected and invertase could hydrolyze sucrose into glucose for generation of glucometer signal output, dual-response for accurate detection of Dam MTase was realized. In the presence of Dam MTase, the methylation of hairpin probe 1 (HP1) occurred and thus caused the cleavage of HP1 assisted by a restriction endonuclease (DpnI) to produce the binding sequences. The binding sequences then hybridized with the electrode-assembled HP2 to expose their sticky termini which sequentially hybridized with the Invertase/MOFs-tethered capture probes. Finally, the electrodes were incubated with a sucrose solution, followed by the separate electrochemical and glucometer detection. The present assay brought good performance which could detect Dam MTase activity as low as 0.001 U mL-1 with wide linear range and good selectivity against other cytosine MTase (M.SssI MTase). Moreover, it also owns ability to be potentially applied for the inhibitors screening by utilization of 5-fluorouracil as an inhibitor model. The results imply that our proposed method provides a convenient platform for early cancer diagnosis and therapeutic applications.

Fibrinogen, which is a glycoprotein that circulates in the blood, plays various important biological roles, e.g., in blood coagulation, fibroblast proliferation, angiogenesis, and wound healing. Abnormal levels of fibrinogen in plasma have been identified as a key biomarker of a variety of disorders from cardiovascular diseases to hemophilia. Therefore, the development of a quantitative assay for fibrinogen in the blood has emerged as an important issue for the prevention and diagnosis of these diseases. Meanwhile, it is well known that erythrocytes can selectively capture fibrinogen because of the fibrinogen receptor expressed on their plasma membrane. Inspired by these biological interactions, herein, we devised an erythrocyte membrane (EM)-blanketed biosensor based on localized surface plasmon resonance (LSPR) for highly sensitive detection of fibrinogen. By placing the EM onto a nanoparticle-on-substrate, we enhanced the LSPR signal, achieving highly sensitive and selective detection of fibrinogen. We demonstrated that fibrinogen detection is possible over a wide concentration range, 0.001–5.000 mg/mL, which can cover normal and pathological blood fibrinogen levels. In addition, it was verified that the biosensor selectively detects fibrinogen in comparison with other human-blood-plasma components. The nanoplasmonic sensor blanketed with the EM opens up new opportunities for the development of a robust fibrinogen-sensing technology.

In this work, the ZnO nanostars with excellent catalytic performance were firstly used as the coreaction accelerator of luminol-O2 system to construct a biosensor for ultrasensitively detecting microRNA-21 (miRNA-21) in cancer cells. Specifically, ZnO nanostars could expedite the reduction of dissolved O2, generating more reactive oxygen species (ROSs) to extremely promote electrochemiluminescence (ECL) luminous efficiency of luminol. Thus luminol-functionalized Au NPs@ZnO (L-Au NPs@ZnO) nanomaterials were employed as signal probe to fabricate sensing nano-platform for achieving significant ECL emission as "signal on" state. Moreover, upon the addition of a tiny minority of target miRNA-21, massive ferrocene (Fc) could be immobilized on the sensing interface through hybridization chain reaction (HCR) triggered-DNA dendrimers self-assembly, in which Fc consumed dissolved O2 for prominently quenching the ECL emission of signal probe and then reached a "signal off" state. As a result, the biosensor performed a good linearity in 100 aM - 100 pM and a low limit of detection (LOD) down to 18.6 aM. In general, this work utilized a new coreaction accelerator as an efficient amplification approach for ultrasensitively detecting target analyses, providing a promising approach in luminol-centric ECL bioanalysis fields.

Highly sensitive phenol biosensor was developed by using well-dispersed carbon nanotubes (CNTs) in enzyme solution and adding CNTs in enzyme electrodes. First, the intact CNTs were dispersed in aqueous tyrosinase (TYR) solution, and TYR molecules were precipitated and crosslinked to prepare the sample of enzyme adsorption, precipitation and crosslinking (EAPC). EAPC exhibited 10.5- and 5.4-fold higher TYR activity per mg of CNTs as compared to enzyme adsorption (EA) and enzyme adsorption/crosslinking (EAC), respectively. EAPC retained 29% of its initial activity after incubation at 40 °C for 128 h, while EA and EAC showed no residual activities, respectively. In biosensing a model phenolic compound of catechol, the sensitivities of EA, EAC and EAPC electrodes on glassy carbon electrode (GCE) were 34, 281 and 675 µA/mM/cm2, respectively. When 90 w/w% CNTs were added to the enzyme electrodes, the sensitivities of EA, EAC, and EAPC electrodes were 146, 427, and 1160 µA/mM/cm2, respectively, and the EAPC electrode showed a 2.3-fold increase in sensitivity upon CNT addition. Catechol and phenol could also be detected by EAPC on the screen-printed electrode (SPE), with sensitivities of 1340 and 1170 µA/mM/cm2, respectively. The sensitivity of EAPC-SPE for phenol detection in the effluent from real municipal wastewater treatment plant was 1100 µA/mM/cm2. The sensitivity of EAPC-SPE retained 74% of its initial sensitivity after incubation at 40 °C for 12 h. The combination of EAPC immobilization and CNT addition has great potential for application in the development of sensitive enzyme biosensors for various analytes and phenols in water environments.

In this work we discussed a label-free biosensing application of long-period gratings (LPGs) optimized in refractive index (RI) sensitivity by deposition of thin tantalum oxide (TaOx) overlays. Comparing to other thin film and materials already applied for maximizing the RI sensitivity, TaOx offers good chemical and mechanical stability during its surface functionalization and other biosensing experiments. It was shown theoretically and experimentally that when RI of the overlay is as high as 2 in IR spectral range, for obtaining LPGs ultrasensitive to RI, the overlay's thickness must be determined with subnanometer precision. In this experiment the TaOx overlays were deposited using Atomic Layer Deposition method that allowed for achieving overlays with exceptionally well-defined thickness and optical properties. The TaOx nano-coated LPGs show RI sensitivity determined for a single resonance exceeding 11,500 nm/RIU in RI range nD= 1.335–1.345 RIU, as expected for label-free biosensing applications. Capability for detection of various in size biological targets, i.e., proteins (avidin) and bacteria (Escherichia coli), with TaOx-coated LPGs was verified using biotin and bacteriophage adhesin as recognition elements, respectively. It has been shown that functionalization process, as well as type of recognition elements and target analyte must be taken into consideration when the LPG sensitivity is optimized. In this work optimized approach made possible detection of small in size biological targets such as proteins with sensitivity reaching 10.21 nm/log(ng/ml).

In this work, an ultrasensitive electrochemiluminescence (ECL) biosensor was constructed using poly- L -lysine (PLL) as a novel co-reactant of luminol and poly(luminol/aniline) nanorods loaded reduced graphene oxide (PLA@rGO) as nanoprobe, which enable highly sensitivity detection of glutathione (GSH). To the best of our knowledge, it is the first time that PLL was used for the co-reactant of luminol. Notably, about a 5-fold enhancement was obtained compared with the individual PLA@rGO using GCE. Due to the remarkable quenching effect between the excited state of PLL and the reduced form of GSH in the ECL system of luminol/PLL, the ECL sensing platform exhibited wide linear ranges of 1.0 × 10−9–1.0 × 10−4 M and 1.0 × 10−4–1.0 × 10−2 M and a low detection limit of 7.7 × 10−10 M. Simultaneously, the biosensor was also successfully applied to detect GSH in human serum sample with high recoveries. Hence, this work would open a new platform for the wide application of PLL in immunoassay and various sensors.

A bimetallic NiCo-based metal-organic framework (NiCo-MOF) was pyrolyzed into a novel composite comprising NiCo2O4 spinel, CoO, and metallic Co/Ni nanoparticles embedded with carbon nanotubes at high temperature 700 °C under N2 atmosphere (represented by NiCo2O4/CoO@CNTs), whereas organic ligands were almost decomposed in H2 atmosphere, leading to absence of carbon nanotubes (denoted by NiCo2O4/CoO). The feasibility of using the composite as efficient bioplatform for immobilizing the probe DNA of human immune deficiency virus-1 (HIV-1) in the electrochemical detection of the HIV-1 DNA was explored. Compared with the pristine NiCo-MOF and NiCo2O4/CoO, the NiCo2O4/CoO@CNTs composite exhibited high electrochemical activity, good biocompatibility, and strong bioaffinity toward the probe DNA. Electrochemical measurements demonstrated that the NiCo2O4/CoO@CNTs-based bioassay displayed superior sensing performances, giving an ultralow detection limit of 16.7 fM toward HIV-1 DNA over the linear range of 0.1 pM to 20 nM; possessing high selectivity even against noncomplementary and two-base mismatch sequences; exhibiting good stability, reproducibility, repeatability and applicability in the application of detecting human serum samples. Thus, the present strategy can broaden the application of MOFs and their derivatives in various fields of biosensing.

Monitoring superoxide anions in living cells have attracted much academic and biomedical interest due to their important role in metabolic processes. Herein, we confined ultra-small nano-Mn3(PO4)2 in chitosan and designed a unique puffy woven sphere consisted by nanowires. Further constructed an effective in situ detection chip using the as-synthesized nano-Mn3(PO4)2-chitosan for electrochemical sensing of superoxide anions from murine breast tumor cells (4T1). The excellent biocompatibility of chitosan and large size of the Mn3(PO4)2-chitosan spheres greatly reduced the damage and toxicity of the detection interface to the living cells, while the ultra-small nano-Mn3(PO4)2 in chitosan could effectively catalyze the superoxide anions released from cells. The nano-Mn3(PO4)2-chitosan-based sensor exhibited high sensitivity (1.6 μA μM−1), low detection limit (9.4 nM at S/N = 3) and good selectivity for O2•−. After cell culture on the surface of nano-Mn3(PO4)2-chitosan based electrode. As a miniature analytical and sensing platform, results further suggest that the prepared chip offers a more sensitive detective superoxide anions (O2•−) released from 4T1 cell lines than traditional electron paramagnetic resonance (EPR) analysis.

This study describes an environmental biosensor for real time toxicity monitoring, which exploits high sensitivity of a microbial fuel cell (MFC) to variations in concentrations of electron donors and acceptors. Fast biosensor response to changes in total heavy metal concentration of a mining rock drainage was observed in laboratory tests with acceptable repeatability and a coefficient of determination (R2) of 0.95–0.97. The biosensor response is attributed to interference of heavy metals with the activity of electroactive microorganisms. Biomolecular analysis of the anodic electroactive biofilms showed significant population differences between microbial populations of the biosensor exposed to heavy metals and a non-exposed (control) biosensor. Furthermore, the biosensor outputs were highly correlated (R2 = 0.92) with the results of the Microtox toxicity assay. The results of this study contribute towards the development of a simple MFC-based biosensor capable of detecting, in real-time, changes in environmental conditions and providing a tool for on-site toxicity monitoring.

A non-enzymatic and highly electrocatalytic H2O2 biosensor was proposed by using a novel electrode composed of hemin-capped biomineralized gold nanoparticles (Hem@AuNPs), reduced graphene oxide (rGO) and chitosan (CS). Owing to the excellent electrocatalytic activity of Hem@AuNPs and great conductivity of rGO, this developed biosensor is capable of ultrasensitive measuring H2O2 in real-time. In addition, the introduction of CS resulted in a film on the electrode, which can enhance the stability by protecting the biosensor from external disturbances. Taking advantages of the peroxidase-like activities of the nanohybrids, the developed electrode exhibited outstanding electrochemical performance toward H2O2 with high selectivity, fast response, superior sensitivity and good stability. More importantly, the lower determination limit of 9.3 nM and wider linear ranges of 5 orders of magnitude enable this biosensor to detect H2O2 releasing from living Hela cells accurately. This work provides tremendous potential for real-time monitoring the secretion of H2O2 in living cells.

Research in wearable electronics has paved the way for next-generation technology, sought to create point-of-care biosensors that combine chemical sensing on a biocompatible platform with a broad range of applications in human health monitoring. Despite significant progress, the microspatial mechanical mismatch and fluid-impermeable interface presented between skin and the electronics create adscititious problems in device lamination, conformality, and long-term monitoring. Herein, we engineered a skin-inspired, deterministically patterned, electrochemical biosensor that can be fully integrated with the curvilinear surface of the human body, while mechanically adapting to the natural stresses applied to the skin and allowing the mass transfer of gas and fluids. In particular, we developed mechanically-compliant lattice-structured biosensors for the continuous evaluation of lactate and oxygen. Systematic studies of the sensor performance were evaluated with variations in polymeric membranes and its ability to withstand commonplace harsh, multiaxial stresses.

Fluorescent copper nanomaterials (CuNMs), including copper nanoparticles (CuNPs) and copper nanoclusters (CuNCs), become more and more popular with the abundant raw materials and low cost. A wide range of applications has been explored due to their fascinating properties such as low toxicity, remarkable water solubility, facile synthesis, large Stokes shifts, and good biocompatibility. As a kind of genetic material, DNA exhibits its molecular recognition function and diversity. The marriage between CuNMs and DNA endows DNA-templated CuNMs (DNA-CuNMs) with unique properties such as fluorescence, electrochemiluminescence and catalytic features. In this review, we summarize the synthesis and recent applications of DNA-CuNMs. Fluorescent CuNMs can be grown on various DNA scaffolds with special sequence design. T base plays an important role in the formation of CuNMs on DNA templates. These fluorescent DNA-CuNMs hold great prospect in logic gate construction, staining and biosensing of DNAs and RNAs, ions, proteins and enzymes, small molecules and so on.

Lateral flow immunoassay (LFIA) is a class and widespread applied point-of-care biosensor in the rapid monitoring field. To address the matched antibodies and antibody labeling dependence in the conventional LFIAs, in this work, an innovative label-free LFIA was proposed for the sensitive detection of Salmonella enteritidis (S. enteritidis) by introducing a new nanoparticles-bacteria-antibody sandwich strategy in the sensor. Surface positively charged nitrogen-rich carbon (pNC) nanoparticles, synthesized via calcination and etching reactions, were used as adsorbent to capture bacteria as well as for generating signals. In the presence of target pathogens, bacterial cells could combine with pNC through electrostatic interaction and hydrogen bonding, then the complex would be captured specifically by the anti-bacteria monoclonal antibody (McAb) coated on the test line (T-line). With the accumulation of nanoparticles-bacteria, the color on T-line would be gradually deepened from nearly colorless to deep black. Importantly, the pNC-based immunoassay could exhibit high sensitivity for target pathogens detection with a linear range of 102–108 cfu mL−1 and a low detection limit of 102 cfu mL−1. Furthermore, this system was validated preliminarily to screen S. enteritidis in different food samples with recoveries ranging from 85% to 110%. Taking advantages of simplicity, label-free, convenience, and sensitivity, the pNC-based LFIA has the application potential for pathogenic microorganisms monitoring in food safety and early clinical diagnosis fields.

A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 ± 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors.

Protein-inorganic nanoflowers have been extensively used for sensing and biosensing applications by virtue of the signal enhancement of protein component---enzyme. Can the inorganic component of protein-inorganic nanoflowers be employed to amplify signal transducing for enzyme-free detection? In this work, a new kind of BSA-antibodies-copper phosphate hybrid nanoflowers (BSA-Ab2-Cu3(PO4)2) has been prepared by one-pot biomimetic mineralization process as signal enhancer for enzyme-free electrochemical immunoassay. C-reactive protein (CRP) has been chosen as a model biomarker. To the best of our knowledge, it is the first trial using the inorganic component---phosphate ions of BSA-Ab2-Cu3(PO4)2 for transducing electrochemical readout, which features the following advantages: (1) the three-dimensional hierarchical porous nanoflower morphology with a high specific surface area could load more antibodies, and BSA for blocking non-specific sites, greatly increasing the sensitivity of the fabricated immunosensors, (2) the Cu3(PO4)2 hybrid nanoflowers can supply a huge amount of phosphate anions to react with molybdate yielding molybdophosphate precipitates and generating redox currents for more robust enzyme-free electrochemical signal readout. The fabricated immunosensor has exhibited good detection performance with a linear range of 5 pg/mL–1 ng/mL and a limit of detection of 1.26 pg/mL. Moreover, our method has presented good feasibility for clinical sample analysis.

Ion channel is a pore-forming membrane protein that allows ions to pass through the cell membrane, which is essential for the continuation of life. Analysis of ion channel characteristics at the single cell level will help to study the role of cellular heterogeneity in disease progression and cellular signaling processes. In this study, we fabricate a photocleavable and entropy-driven reaction based electrochemical biosensor for ultrasensitive detection of human ether-a-go-go related gene (hERG) potassium channel activity on HEK293 cell. We employed an antibody-DNA1 to conjugate the hERG channel in the cell membrane via antibody-antigen reaction. The release of the DNA1 by photocleavable reaction will trigger an amplification reaction by using the Exonuclease III (Exo III) to generate intermediate DNA. In addition, two hairpin DNA (DNA3 and DNA4) was employed for the signal amplification. We well designed a toehold on DNA3 for intermediate DNA hybridization to form double-strand DNA that opens the DNA3 hairpin. The free DNA3 exposed the relocked toehold domain to open the DNA4. After the entropy-driven toehold-mediated displacement amplification reaction by using intermediate DNA, DNA4 hybridized with DNA3 effectively, making the ferrocene labeled on the 5'-termini DNA4 close to the Au electrode surface to produce the electrochemical response. Then, the displaced intermediate DNA was released from the cell surface into solution for the next entropy-driven reaction. After two steps amplification reaction, one ion channel triggered thousands of DNA3/DNA4 duplex on the biosensor surface. By using this biosensor, electrochemical curve of hERG ion channels on a single cell was obtained.

An efficient and new electrochemical biosensor for detection of DNA damage, induced by the interaction of the hybrid anti-cancer compound (7ESTAC01) with DNA, was studied by differential pulse voltammetry (DPV). The biosensor consists of a Stem-Loop DNA (SL-DNA) probe covalently attached to the gold electrode (GE) surface that hybridizes to a complementary DNA strand (cDNA) to form a double-stranded DNA (dsDNA). The interaction and DNA damage induced by 7ESTAC01 was electrochemically studied based on the oxidation signals of the electroactive nucleic acids on the surface of the GE by DPV. As a result, the SL-DNA/GE and dsDNA/GE were tested with the reduced 7ESTAC01, showing the voltammetric signal of guanine and adenine, increase in the presence of 7ESTAC01. Under optimum conditions, the dsDNA/GE biosensor exhibited excellent DPV response in the presence of 7ESTAC01. The bonding interaction between 7ESTAC01 and calf thymus DNA (ctDNA) was confirmed by UV-Vis absorption spectroscopy, dynamic simulations (performed to investigate the DNA structure under physiological conditions), and molecular docking. Theoretical results showed the presence of hydrogen bonding and intercalation in the minor groove of DNA, involving hydrophobic interactions.

This article is clearly presenting the development of a biosensor for human factor IX (FIX) to diagnose the blood clotting deficiency, a so-called ‘Royal disease’ using an interdigitated electrode (IDE) with the zinc oxide surface modification. Gold nano-urchins (GNUs) with 60 nm in diameter was integrated into a streptavidin-biotinylated aptamer strategy to enhance the active surface area. Two different comparative studies have been done to validate the system to be practiced in the current work holds with a higher capability for the high-performance sense. Whereby, the presence and absence of GNUs in the aptasensing system for FIX interaction were investigated using the amperometric measurement, using a linear sweep voltage of 0–2 V at 0.01 V step voltage. The detection limit was 6 pM based on 3σ calculation when GNUs integrated aptamer assay was utilized for FIX detection, which shows 8 folds sensitivity enhancement comparing the condition in the absence of GNU and 50 folds higher than sensitive radio-isotope and surface plasmon resonance assays. Albeit, the surface and molecular characterizations were well demonstrated by scanning electron microscopy, atomic force microscopy, 3D nano-profilometry and further supports were rendered by UV–Vis spectroscopy and Enzyme-linked apta-sorbent assay (ELASA). Furthermore, the spiking experiment was done by FIX-spikes in human blood serum in order to demonstrate the stability with a higher non-fouling.

In this study, a dual-type responsive electrochemical biosensor was developed for the quantitative detection of α2,6-sialylated glycans (α2,6-sial-Gs), a potential biomarker of tumors. The gold nanorods (AuNRs), which exhibited great specific surface area, as well as good biocompatibility, was synthesized by the way of seed growth method. Furthermore, a biotin-streptavidin (biotin-SA) system was introduced to improve the immunoreaction efficiency. Accordingly, a label-free biosensor was fabricated based on AuNRs-SA for the quick detection of α2,6-sial-Gs by recording the signal of differential pulse voltammetry (DPV). Furthermore, to expand the ultrasensitive detection of α2,6-sial-Gs, a carboxylated single-walled carbon nanohorns/sulfur-doped platinum nanocluster (c-SWCNHs/S-PtNC) was synthesized for the first time as a novel signal label, which showed an excellent catalytic performance. The usage of c-SWCNHs/S-PtNC could significantly amplify the electrochemical signal recorded by the amperometric i-t curve. Herein, a sandwich type biosensor was constructed by combining the AuNRs-SA on the electrode and c-SWCNHs/S-PtNC (signal amplifier). The label-free biosensor possessed a linear range from 5 ng mL−1 to 5 μg mL−1 with a detection limit of 0.50 ng mL−1, and the sandwich-type biosensor possessed a wide linear range from 1 fg mL−1 to 100 ng mL−1 with a detection limit of 0.69 fg mL−1. Furthermore, the biosensor exhibited excellent recovery and stability, indicating its potential for use in actual samples.

Developing low-cost, portable and simple analysis tools is of vital importance for food safety point-of-care testing. Therefore, herein, a new low-cost, simple to fabricate, disposable, electrochemical mast cell-based paper sensor is proposed and developed to sensitively determine the major milk allergen casein. Then, a graphene (GN)/carbon nanofiber (CN)/ Gelatin methacryloyl (GelMA) composite material with high conductivity and good biocompatibility was modified on the cell-based paper sensor to improve the electrical conductivity and provide a sensing recognition interface for the immobilization of rat basophilic leukemia (RBL-2H3) mast cells. The cyclic voltammetry and differential pulse voltammetry measurement of the mast cells in the paper sensor revealed an irreversible anodic peak, whose peak current is proportional to the number of cells in the range from 1 × 102 to 1 × 108 cells/mL. For the milk allergen detection tests, mast cells exposed to the casein caused a significant reduction in the current signal, displaying an inverse dose-dependent relationship. The developed cell sensor exhibited a range of linearity between 1 × 10−7 and 1 × 10−6 g/mL of casein with a detection limit of 3.2 × 10−8 g/mL and a great reproducibility and selectivity. The electrochemical responses obtained using the cell-based paper sensor were well consistent with the conventional detection assay, with good stability and reproducibility. Therefore, a simple and novel electrochemical method for food allergens detection was developed, demonstrating its potential application in the food safety determination and evaluation.

In the field of label-free biosensing, various transducer materials and strategies are under investigation to overcome the Debye-screening limitation of charged biomolecules. We demonstrate an in-line, impedimetric aptasensor with reduced graphene-oxide (rGO) thin films as transducers to detect prostate specific antigens (PSA) in a physiological buffer solution. Unlike classical electrochemical impedance spectroscopy (EIS), this direct, label-free and fully-electronic biosensor approach does not need any redox markers. As specific capture molecules, short anti-PSA aptamers ensured a close binding of the target molecules to the transducer surfaces. Results showed a limit of detection smaller than 33 pM of PSA and a wide detection range from 0.033 to 330 nM fully covering the clinically relevant range of PSA (0.115–0.290 nM). This promising performance can be attributed to the bipolar electronic transport characteristics of the ultra-thin rGO layers similar to pristine graphene. The attachment of target biomolecules to the films changes the resistance of the rGO thin films. Such an in-line EIS configuration with rGO thin films opens promising prospects for biosensing beyond the Debye-screening limitation, which is a major challenge for conventional semiconductor field-effect devices towards clinical applications.

Mucin 1 protein (MUC1) is a membrane-associated glycoprotein overexpressed in the majority of human malignancies and considered as a predominant protein biomarker in cancers. Owing to the crucial role of MUC1 in cancer dissemination and metastasis, detection and quantification of this biomarker is of great importance in clinical diagnostics. Today, there exist a wide variety of strategies for the determination of various types of disease biomarkers, especially MUC1. In this regard, aptamers, as artificial single-stranded DNA or RNA oligonucleotides with catalytic and receptor properties, have drawn lots of attention for the development of biosensing platforms. So far, various sensitivity-enhancement techniques in combination with a broad range of smart nanomaterials have integrated into the design of novel aptamer-based biosensors (aptasensors) to improve detection limit and sensitivity of analyte determination. This review article provides a brief classification and description of the research progresses of aptamer-based biosensors and nanobiosensors for the detection and quantitative determination of MUC1 based on optical and electrochemical platforms.

Paper-based biosensors are promising for low-cost diagnostics. However, its widespread use has been hampered due to a lack of sensitive detection methods that can be easily implemented on paper substrates. On the other hand, single-walled carbon nanotubes (SWNTs) -based chemiresistive biosensors are gaining popularity as label-free, highly sensitive biosensors. However, traditional SWNT-based chemiresistors need to be more affordable for use in resource-limited settings. In this study, we report fabrication, optimization and analytical characterization of a chemiresistive biosensor on paper for label-free immunosensing. We synthesized a water-based ink using pyrene carboxylic acid (PCA) through non-covalent π-π stacking interaction between PCA and SWNTs. The PCA/SWNTs ink concentration can reach ~4 mg mL−1 and was stable at room temperature for one month. We introduced a combination of wax printing and vacuum filtration to fabricate the hydrophilic channels and the well-defined PCA/SWNTs ink deposition on paper in a facile manner requiring no additional masks or stencils. Specific antibodies were then functionalized on the PCA/SWNTs. Quantitative and selective detection of human serum albumin (HSA) is demonstrated with a limit of detection (LOD) of 1 pM. This low LOD is attributed to the porous structure of the paper surface, which can accommodate more SWNTs. Furthermore, the hydroxyl group-containing cellulose fibers help connect the SWNTs into an electrical network. The paper-based chemiresistive biosensor proposed here is easy to fabricate, and designed for rapid, sensitive and selective detection of HSA. This work provides a potential platform for automated, disposable paper-based biosensors with multiplexed detection capability and microfluidic controls.

How to obtain sufficient functional olfactory receptors and coupled to transducers with high efficiency are crucial to biomimetic olfactory-based biosensors. In this study, a cell-free expression system was employed to prepare functional olfactory receptors that were utilized as sensitive elements for biomimetic olfactory receptor-based biosensors. A nematode olfactory receptor, ODR-10, was used as a model of olfactory receptors and expressed in Escherichia coli (E. coli) cell-free expression system. To improve the coupling efficiency and obtain the on-chip purification, a His6-tag was expressed as a fusion to ODR-10, which makes the expressed ODR-10 capable of selectively binding to the sensor surface modified with anti-His6-tag aptamers. Electrolyte-insulator-semiconductor (EIS) sensors were utilized as the transducer to measure the capacitance changes induced by the ODR-10 responding to its natural ligand, diacetyl. The results show that ODR-10 was successfully expressed using E. coli cell-free expression system and the expression could be promoted by adding 0.5% Brij58 as the detergent. Capacitance measurement results indicate that this olfactory receptor-based biosensor can detect diacetyl with high specificity and sensitivity. Concentration-dependent linear response to diacetyl ranging from 0.01 nM to 1 nM was obtained. The detection limit was as low as 0.01 nM. All the results demonstrated that the cell-free expression system provides a new approach for the preparation of functional olfactory receptors, which have great potential to be applied in biomimetic sensors towards chemical sensing.

Herein, a near-infrared (NIR) light-responsive imprinting biosensor with excellent conductivity and tensibility was designed by incorporation graphene oxide/polyaniline (GO/PANI) with thermo-responsive poly(N-isopropylacrylamide) hydrogel (PNiPAAm) on a glassy carbon electrode (GCE). In this design, polyaniline (PANI) nanofiber modifies with graphene oxide (GO) acts as a physically cross-linker, providing hydrogen bond interaction with amide groups in the PNiPAAm. It is functioned to enhance the strength of imprinted hydrogel networks. Thus, the imprinted hydrogel biosensor incorporation of GO/PANI nanocomposite exhibited excellent mechanical performance and NIR light-responsive characteristic. As a NIR radiation trigger gate, the obtained biosensor not only has a function of IR-based cleaning toward bovine serum albumin (BSA) in the absence of elution solution, but also a function of proteins releasing and uptaking, basing on reversibly conformational changes with 808 nm NIR light. Simultaneously, the responsive processes were electronically monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and verified by scanning electron microscopy (SEM). Moreover, the proposed GO/PANI nanocomposite imprinted biosensor exhibited excellent characteristics along with high conductivity and tensibility, long-term stability, and wide linear range, performing great promising for preparing remote NIR light-driven extraction protein smart devices.

In this work, a photoactive material, Graphdiyne (GDY) loaded with AuNPs (AuNPs-GDY), was successfully synthesized. The fabricated material made use of the natural band-gap structure of GDY, which could produce hole-electron pairs and the plasmon resonance effect of AuNPs to obtain a high photoelectrochemical (PEC) response. AuNPs-GDY PEC response changed with the mass ratio of GDY to tetrachloroauric acid. When the mass ratio of GDY to tetrachloroauric acid was 1:2.5, AuNPs-GDY exhibited the best PEC performance. Thus, the best one was selected as the photoactive material to establish a PEC biosensor for microRNA detection. The PEC biosensor used the alkaline phosphatases as catalyzer to generate ascorbic acid in situ, which provided a low background signal and a high PEC response. The cancer marker, MicroRNA let-7a, was chosen as a target model. Under optimal condition, potential 300 mV and pH 8.0, the PEC biosensor had a detection limit of 3.3 × 10–19 M and a good linearity with microRNA let-7a concentration ranged from 1.0 × 10–18 M to 1.0 × 10−10 M. This PEC biosensor opened a promising platform using GDY to fabricate analytical method and detect microRNA at ultralow levels for diagnoses.

MicroRNAs have been proved to be the biomarker for early detection of pancreatic cancer and the precisely quantitation of the MicroRNA-10b in the blood samples even can distinguish pancreatic cancer from chronic pancreatitis (CP) and normal controls (NC). In this study, we developed a DSN-assisted dual-SERS biosensor for microRNA-10b in exosome and residual plasma of blood samples detection based on the Fe3O4 @Ag-DNA-Au@Ag@DTNB (SERS tag) conjugates. In presence of target microRNA, it can hybridized with the complementary DNA probes. DSN enzyme was then added to selectively cleaves the DNA probe of the DNA/microRNA duplex, SERS tags can be released from the Fe3O4@Ag and SERS intensity quenching can be triggered, the released microRNA can enter the cycle to decluster other DNA and SERS tags. Due to the dual-SERS enhancement of the Fe3O4@Ag-SERS tag conjugates and the recycling signal amplification, a detection limit of 1 aM with single-base recognition can be performed by one step. The target microRNA in plasma-derived exosome and residual supernatant plasma of blood samples from pancreatic ductal adenocarcinoma (PDAC), chronic pancreatitis (CP) and normal controls (NC) were directly quantified and significant SERS signal distinction can be found among them. The precise quantitation, one-step and one-pot operation can ensure this assay a promising future for point-of-care cancer diagnosis technology.

L- Glutamate is the main excitatory neurotransmitter in the central nervous system and hyperglutamatergic signaling is implicated in neurological and neurodegenerative diseases. Monitoring glutamate with a glutamate oxidase-based amperometric biosensor offers advantages such as high spatial and high temporal resolution. However, commercially-available glutamate biosensors are expensive and larger in size. Here, we report the development of 50 03BCm diameter biosensor for real-time monitoring of L-glutamate in vivo. A polymer, poly-o-phenylenediamine (PPD) layer was electropolymerized onto a 50 μm Pt wire to act as a permselective membrane. Then, glutamate oxidase entrapped in a biocompatible chitosan matrix was cast onto the microelectrode surface. Finally, ascorbate oxidase was coated to eliminate interferences from high levels of extracellular ascorbic acid present in brain tissue. L-glutamate measurements were performed amperometrically at an applied potential of 0.6 V vs Ag/AgCl. The biosensor exhibited a linear range from 5 to 150 μM, with a high sensitivity of 0.097 ± 0.001 nA/μM and one-week storage stability. The biosensor also showed a rapid steady state response to L-glutamate within 2 s, with a limit of detection of 0.044 μM. The biosensor was used successfully to detect stimulated glutamate in the subthalamic nucleus in brain slices and in vivo. Thus, this biosensor is appropriate for future neuroscience applications.

Cortisol is an hormone that regulates blood pressure, glucose levels and carbohydrate metabolism in humans. Abnormal secretion of cortisol can cause various symptoms closely linked to psychological and physical health. In this study, high-performance field-effect transistor (FET)-based biosensors for cortisol detection were fabricated from N-doped multidimensional carbon nanofibers. N a n o f i b e r morphology was controlled by tailoring the pressure conditions during vapor deposition polymerization (VDP). Thereafter, conductive channels o f FET were completed by thermal annealing, acid treatment, and antibody attachment. Changes associated with chemical processes were characterized by v a r i o u s i n s t r u m e n t s. The resulting transducers exhibited a rapid response toward cortisol molecules with accurate selectivity, stable reusability, and high sensitivity. M i n i m u m d e t e c t i o n l e v e l were as low as 100 aM with a wide linear detection range of 100 aM to 10 nM due to the large surface area of the transducer and a correspondingly high number of antibody labels. The response and applicability of these cortisol biosensors were also assessed using saliva as a test matrix.

A novel photoelectrochemical (PEC) immunosensor was successfully constructed for N6-methyladenine (m6A) detection based on the photoactive materials of black titanium dioxide (B-TiO2) and bismuth trioxide (Bi2O3) and the signal amplification unit of [Ru(bpy)3]2+-doped metal organic framework (MOF). The Bi2O3/B-TiO2/ITO electrode was first fabricated, then decorated with gold nanoparticles (AuNPs) which provided sites for anchoring m6A antibodies. After the capture of m6A via immunoreaction with the antibody, the Zr-based metal organic framework (UiO-66)-[Ru(bpy)3]2+ compound was further attached specifically to the phosphate group of m6A. With visible light irradiation, a large and stable photocurrent response was produced in the presence of ascorbic acid (AA). Under optimized experimental conditions, the linear range of the PEC biosensor was 0.05–30 nM, with a low detection limit of 0.0167 nM (S/N = 3). This method showed high specificity, selectivity, stabilization and repeatability. Moreover, it was successfully used for the detection of m6A in rice seedling leaves that had been subjected to heavy metal treatment during their development.

We fabricate a novel electrochemical biosensor based on the specific thymine-Hg2+-thymine (T-Hg2+-T) base pair for the highly sensitive detection of mercury ions (Hg2+) and utilize toluidine blue (TB) as a redox indicator that is combined with a hybridization chain reaction (HCR) for signal amplification. The dandelion-like CuO (D-CuO) microspheres that were assembled using Au nanoparticles were first introduced as support materials, which produced more active sites for the thiolated probe (P1) combination. Then, the presence of Hg2+ induced P1 to hybridize with the other oligonucleotide (P2) through Hg2+-mediated T-Hg2+-T complexes. In addition, the partial sequence of P2 acted as an initiator sequence, which led the two hairpin DNA (H1 and H2) strands to collectively form the extended double-strand DNA through the HCR process on the electrode surface. TB was employed to interact with the double strands and produce an efficient electrochemical signal. The proposed strategy combined the amplification of the HCR and the inherent redox activity of TB and utilized D-CuO/Au composites, which exhibited high sensitivity for Hg2+ determination. Under the optimum conditions, the proposed biosensor showed a prominent response for Hg2+, including a linear range from 1 pM to 100 nM and a detection limit of 0.2 pM (S/N = 3). Moreover, the new biosensor proved its potential application for trace Hg2+ determination in environmental water samples.

Enzymatic and non-enzymatic amperometric glucose sensors based on nanostructured Au-Ni alloy were prepared and compared in their performance. The hierarchically structured Au-Ni surface was merely used for the non-enzymatic glucose sensor, while glucose oxidase attached poly-3′(benzoic acid) −2,2′:5′,2′- terthiophene (pTBA) formed on the alloy surface was used as the enzymatic sensor. The fabricated sensor was characterized using surface analysis and electrochemical experiments. In case of the enzymatic sensor, the anodic current of H2O2 generated from the enzyme reaction was used as the analytical signal, while the direct oxidation of glucose was observed on a mere Au-Ni alloy electrode without enzyme immobilization, which shows an excellent catalytic oxidation of glucose even in physiological pH. The potential pulse pretreatment of the sensor surfaces improved the performance, which allowed both the sensors reproducible and reusable (enzymatic sensor: coefficient of variation = 1.82%, n = 5, non-enzymatic: coefficient of variation = 2.93%). The enzymatic biosensor reveals the advantages of increased sensitivity, selectivity, and stability, compared with the non-enzymatic sensor. The linear range of enzymatic sensor was attained from 1.0 µM to 30.0 mM with a detection limit of 0.29 μM. The reliabilities of the sensors were also demonstrated through the glucose analysis in human blood samples, and the result was compared with the commercially available glucometer.

A highly sensitive and selective glutamate biosensor using glutamate Oxidase (GlUtOx) immobilized platinum nanoparticle (PtNP) decorated multiwall carbon nanotube (MWCNTs)/polypyrrole (PPy) composite on glassy carbon electrodes (GC) is demonstrated. PtNP decorated MWCNTs (Pt-MWCNTs), PPy and Pt-MWCNTs/PPy composite were characterized by Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD) and Raman analysis to confirm the formation of the nanocomposite. The glutamate Oxidase (GlUtOx) was immobilized on a GC/Pt-MWCNTs/PPy and characterized by the cyclic voltammetry (CV) and impedance spectroscopy (EIS) analysis. The fabricated L-glutamate biosensor exhibited high sensitivity (723.08 µA cm−2 mM−1) with less response time (3 s) with a detection limit of 0.88 µM. The dynamic range from 10 to 100 µM with a correlation coefficient (R2) of 0.985 was observed for the L-glutamate biosensor. The analytical recovery of added L-glutamate acid (50 and 100 μM) in human serum soup were 96.1% and 97.5% respectively. The enzyme immobilized GC/Pt-MWCNTs/PPy/GlUtOx bioelectrode lost 12 .6% and 23.8% of its initial activity after 30 days when stored at − 20 °C and 4 °C respectively.

The synthesis and employment of volatile toxic compounds as chemical weapons with a large-scale destructive power has introduced a new insidious threat over the last century. In this framework, the development of wearable sensing tools represents a critical point within the security field, in order to provide early alarm systems. Herein, a novel wearable electrochemical biosensor was developed for the rapid and on-site detection of mustard agents. Since a chemical attack is typically carried out by spraying these volatile agents into air, the sensor was designed in order to be able to measure mustard agents directly in the aerosol phase, further than in the liquid phase. The electrodes were screen-printed onto a filter paper support, which allowed to harness the porosity of paper to pre-load all the needed reagents into the cellulose network, and hence to realise an origami-like and reagent-free device. Mustard agent detection was carried out by monitoring their inhibitory effects toward the choline oxidase enzyme, through the amperometric measurement of the enzymatic by-product hydrogen peroxide. A carbon black/Prussian blue nanocomposite was used as a bulk-modifier of the conductive graphite ink constituting the working electrode, allowing for the electrocatalysis of the hydrogen peroxide reduction. After having verified the detecting capability toward a mustard agent simulant, the applicability of the resulting origami-like biosensor was demonstrated for the rapid and real-time detection of real sulfur mustard, obtaining limits of detection equal to 1 mM and 0.019 g·min/m3 for liquid and aerosol phase, respectively.

Herein, a novel photoelectrochemical (PEC) biosensor was developed for the ultrasensitive detection of microRNA-396a based on a MoS2/g-C3N4/black TiO2 heterojunction as the photoactive material and gold nanoparticles carrying Histostar antibodies (Histostar@AuNPs) for signal amplification. Briefly, MoS2/g-C3N4/black TiO2 was deposited on an indium tin oxide (ITO) electrode surface, after which gold nanoparticles (AuNPs) and probe DNA were assembled on the modified electrode. Hybridization with miRNA-396a resulted in a rigid DNA: RNA hybrid being formed, which was recognized by the S9.6 antibody. The captured antibody can further conjugate with the secondary IgG antibodies of Histostar@AuNPs, thereby leading to the immobilization of horse radish peroxidase (HRP). In the presence of HRP, the oxidation of 4-chloro-1-naphthol (4-CN) by H2O2 was accelerated, producing the insoluble product benzo-4-chlorohexadienone on the electrode surface and causing a significant decrease in the photocurrent. The developed biosensor could detect miRNA-396a at concentrations from 0.5 fM to 5000 fM, with a detection limit of 0.13 fM. Further, the proposed method can also be used to investigate the effect of heavy metal ions on the expression level of miRNAs. Results suggest that the biosensor developed herein offers a promising platform for the ultrasensitive detection of miRNA.

The energy transfer efficiency, strongly depending on the distance of donor–acceptor pair, is always a crucial factor for the construction of elegant electrochemiluminescence resonance energy transfer (ECL-RET)-based biosensors. In this paper, a novel and efficient ECL-RET in 2D/2D heterostructured g-C3N4/MnO2 was developed using g-C3N4 nanosheets (g-C3N4 NSs) as energy donor and MnO2 nanosheets (MnO2 NSs) as energy acceptor. In this system, MnO2 NSs in-situ grew on g-C3N4 NSs to form the 2D/2D heterostructure, greatly shortening the distance of the donor–acceptor pair (g-C3N4–MnO2) and thus greatly enhancing the RET efficiency. To demonstrate the performance of the system, a signal “off-on” ECL sensor was designed for glutathione (GSH) analysis. In the absence of GSH, MnO2 significantly quenched the ECL intensity of g-C3N4 owing to ECL-RET in this 2D/2D g-C3N4/MnO2 heterostructure (ECL signal “off”). Upon the addition of GSH, MnO2 was reduced to Mn2+ by GSH and g-C3N4 was released from the heterostructured g-C3N4/MnO2, generating a recovery of ECL intensity (ECL signal “on”). Under the optimal conditions, the designed ECL-RET signal “off-on” sensor realized the sensitive detection of GSH ranged from 0.2–100 μM with the detection limit of 0.05 μM. Furthermore, the as-prepared ECL-RET sensor exhibits good performance in the determination of GSH in human serum samples. The ECL-RET in 2D/2D heterostructure provides an ingenious way for the exploitation of novel ECL biosensing systems.