In this work, the application of carbon quantum dots as known as CQDs for ethanol detection is pioneered, and a multi-fold improvement in gas sensor performance is achieved through the unique electron transport mechanism of carbon quantum dots. The lychee-like SnO2 hollow microspheres and CQDs are prepared by a solvent heat method. The composites are assembled by rapid grinding, ultrasonication, and stirring. The minimum detection limit is 500 ppb. The response/recovery time of the best mass percentage composite is 9 s/16 s to ethanol at 100 ppm with an optimum working temperature of 216℃ in the target gas-sensitive test. Such a fast response speed improvement is ascribed to the excellent electron transfer efficiency of the 5 nm diameter carbon quantum dots (CQDs).

Aggregation of amyloid-β peptide (Aβ) is hypothesized to be the primary cause of Alzheimer's disease (AD) progression. Aβ aggregation has been widely studied using conventional sensing tools like emission fluorescence, electron microscopy, mass spectroscopy, and circular dichroism. However, none of these techniques can provide cost-efficient, highly sensitive quantification of Aβ aggregation kinetics at the molecular level. Among the influences on Aβ aggregation of interest to disease progression is the acceleration of Aβ aggregation by acetylcholinesterase (AChE), which is present in the brain and inflicts the fast progression of disease due to its direct interaction with Aβ. In this work, we demonstrate the ability of a biological nanopore to map and quantify AChE accelerated aggregation of Aβ monomers to mixed oligomers and small soluble aggregates with single-molecule precision. This method will allow future work on testing direct and indirect effects of therapeutic drugs on AChE accelerated Aβ aggregation as well as disease prognosis.

Molecularly imprinted polymer (MIP)-based electrochemical sensors have received growing attention over past decades owing to its robust nature, simple electrochemical control for template removal and cavity regeneration, and go-as-you-please cavity designs into various geometries specific to target analytes. The strength of MIP scheme, in combination with the advantages of electrochemical sensing techniques such as operation simplicity, rapid response, and high sensitivity, provide a synergistic effort to form a highly effective sensing platform suitable for an extremely wide range of interest. In this Review, the introduction of MIP and the comparison between electrochemical sensing methods and other detection strategies are briefly discussed. Then, a broad range of analytes determined using MIP-based electrochemical sensors are listed and critically reviewed, mainly focusing on the applied electrochemical technique, presented linear range along with limit of detection (LOD), biological fluid used in real testing, and pretreatment for real sample. Other sensor performances like selectivity towards analyte, signal repeatability, sensor-to-sensor reproducibility, and stability, are carefully compared with other reported papers. MIP sensors fabricated via the nanoMIP technology, and the ones integrated with portable analyzers, are given in more details as good results are always observed in such instances. Finally, a conclusion regarding recent advances on MIP-based electrochemical sensors is presented, followed by current issues and future development depicted at the last section of the Review.

Abstract not available

Here, we demonstrated the application of a closed bipolar electrode to measure the change in open circuit potential (OCP) of Prussian blue/white as a function of [Cl−] concentration independently of electrode surface area. In this bipolar scheme, a potentiostat holds a constant voltage across two separate cells linked by a shared electrode that is sensitive to [Cl−] on one end and electrodeposited by Prussian blue on the other. As [Cl−] is added to the sample compartment, the ion associates with Ag+ to produce Ag/AgCl, altering the junction potential. This change is balanced electrochemically by a shift in the ratio of Prussian blue/Prussian white. A second potentiostat is used to monitor these changes over the Prussian blue electrode, yielding a for the quantification of chloride. We measured a range of 1.0 mM – 55 mM [Cl−] over various electrode surface areas, demonstrating that the signal response is independent of electrode area. Additionally, the system had the capability to translate signal across a single bipolar electrode while using differently sized electrodes in each compartment, a property that could be beneficial for microarrays or signal amplification.

Glucose detection using sensing materials has lately received interest due to the increased demand for sensitive and selective glucose sensors in pharmaceutical, clinical, and industrial settings. Carbon nanotubes (CNTs) are used intensively as a specific class of effective electrode substances in electrochemical sensing due to their large surface area and interesting physical and electrochemical characteristics. Nickel is an attractive transition metal for glucose electrooxidation with high catalytic activity. In this study, CNT/MoS2/NiNPs nanocomposites with different CNT/MoS2 ratios have been prepared by a hydrothermal reaction. The CNT/MoS2 nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR), and their morphology and composition were characterized by field emission scanning electron microscopy (FESEM). Electrocatalytic activity of the as-prepared nanomaterials towards glucose oxidation was investigated by cyclic voltammetry and amperometry in alkaline media. An excellent sensitivity value of 1212 μA·mM−1·cm−2 with a wide linear range (0.05–0.65 mM), a low detection threshold of 0.197 μM and a short response time (3 s) were achieved by the hybrid CNT/MoS2/NiNPs sensor. Its superior catalytic activity and low cost make this hybrid very promising for applications in the direct sensing of glucose.

Nafion®-nanostructured polyaniline (nsPANi) composite film is prepared using cyclic voltammetry (CV) and immobilized with creatinine deiminase (CD) enzyme and is used to sense creatinine in a buffer phosphate solution. The conditions for preparing Nafion®-nsPANi composite film are optimized by using a mixture design for which the sensitivity is the response. The relationship between the sensitivity of the amperometric creatinine biosensor (y) and the normalized aniline concentration (Y1), HCl concentration (Y2) and scanning rate (Y3) is y = 119.44Y1 + 45.23Y2 + 100.93Y3 + 255.69Y1Y2 + 313.16Y1Y3 + 430.56Y1Y2Y3The maximum sensitivity of an amperometric creatinine biosensor that is constructed using Nafion®-nsPANi composite film in 0.0943 M aniline, 0.9024 M HCl and using a scanning rate of 27.88 mV s − 1 is 2013.2 μA mM−1 cm−2, which is 54.9% better than the sensitivity of a conventional experimental technique. The amperometric creatinine biosensor is 6.60% less sensitive after sensing 0.15 mM creatinine 240 times. The amperometric creatinine biosensor incurs insignificant interference in 0.138 mM urea, 0.085 mM ascorbic acid (AA) and 5.54 mM glucose.

We developed a nitrogen and boron-doped reduced graphene oxide (N, B-HRGO) based chemiresistive sensor to measure dissolved oxygen (DO) in a complex biological medium. The N, B-HRGO modified interdigitated micro electrode arrays (IDE) constructed as a chemiresistor by the drop-cast method. A silicon based fluorinated oxygen permeable membrane protects the surface from the interference and provides a specificity to the sensor. The sensor responded to the DO concentration changes due to modulated surface charge carrier concentration by the adsorbed dissolved oxygen molecule (Oad). For DO concentration range 0–5 mg.L−1 there was nearly 80% change in response for the sensor with membrane. The resistance of the N, B-HRGO film was measured at different DO concentrations in KNO3 solution and during the growth of Amycalotopsis methanolica bacterial fermentation. The study showed that the sensor is sensitive to the oxygen present in the solution and can detect DO consumption in a complex fermentation medium. The effect of water and the electrolyte salt ions present in the electrolyte was studied in detail. It was observed that the adsorption of water molecule increases the sensor resistance, whereas the salt ions have negligible effect on the sensor response. Because of the simple electrode structure, this chemiresistive sensor can measure DO in the micro bioreactors with a volume of few microliters. The N, B-HRGO chemiresistive sensor can also be used for DO measurement in other bioprocess applications.

Active and passive flow control via combining hybrid centrifugal devices holds decisive advantages in microfluidic manipulation. These advantages include but are not limited to multiplexing via single actuation, non-mechanical valving over a wide operational window, ultra low-cost fabrication, complex flow manipulation without requiring specialized surface treatments or surface patterning, and translating established test protocols to a high-throughput analytical platform. However, despite such promises, the complex interplay of various forces makes it extremely difficult to manipulate fluids on such a complex device in a programmable manner. To circumvent these deficiencies, here we present a novel design framework for fluidic manipulation of a drop of blood sample on a hybrid paper – spinning disc device, and translate the concept into a miniature device technology for quantifying blood haematocrit content (volume fraction of red blood cells) as a representative point-of-care hematological testing platform. Exploiting the characteristics of lateral motion under preferential design conditions, we establish a wider window of the capillary flow saturation dynamics as compared to that obtained in standard capillary or centrifugal microfluidics, thereby favouring bio-analytical procedures with high sensitivity and enhanced limit of detection. In a reagent-free framework, this not only puts forward a new detection paradigm for extreme point of care settings but also opens up avenues for advancing the development of novel porous media based on compact disc platforms in the realm of medical diagnostics for the low resource settings, with no impact of an otherwise inevitable weak supply chain and storage facilities of sensitive reagents.

NADH is a cofactor used by a wide range of dehydrogenases. Measurement of the concentration of NADH is widely used to measure the activity of enzymes. Extensive efforts have been made to develop electrochemical sensors for NADH determination at low overpotentials to avoid interferences. The development of an enzymatic electrochemical biosensor for the detection of NADH is described. Nanoporous gold electrodes were utilised for the immobilization of diaphorase and osmium-based polymer Os(bpy)2(PVI). Nanoporous gold electrodes of different pore sizes were manufactured by varying the dealloying temperature. To optimise the enzymatic response, the concentrations of polymer and enzyme, average pore size and the operating temperature were examined with the optimal performance observed using 10 µL of Os(bpy)2(PVI) and 5 µL of diaphorase at concentrations of 6 and 10 mg/mL, respectively, on nanoporous gold electrodes with an average pore size of 5.9 nm. The biosensor showed a high sensitivity of 89.6 µA/cm2 mM, a low LOD of 0.8 µM and a linear range from 5 to 100 µM at a potential of 0.35 V vs Ag/AgCl at a temperature of 40 °C.

Cystatin C (CysC) is a biomarker indicative of renal function, and its comorbidities, including heart failure. Generally, enzyme-linked immunosorbent assay (ELISA) can detect CysC in hours but requires skilled personnel, thorough reagent preparation, and a laboratory setting. Here, we report quantitative lateral flow immunoassays (LFIAs) with two gold nanostructures (AuNSs): gold nanoparticles (AuNPs) and gold nanorods (AnNRs). UV–Vis suggests 358 μg/ml mAbs in AuNPs conjugation and 45 μg/ml mAbs in AuNRs conjugation. With dynamic light scattering (DLS) measuring the hydrodynamic radius (Rh) of monoclonal antibodies (mAbs) – AuNSs conjugates, AuNPs conjugate maximum Rh is 125.9 ± 11.6 nm (1074 µg/ml conjugated mAbs). 895 µg/ml mAbs – AuNRs conjugate gives maximum Rh (55.9 ± 4.5 nm), but 45 µg/ml AuNRs conjugate displays optimum LFIAs performance. Wash-step and bridged structures were introduced for a wider linear range of CysC quantification (up to 12.5 mg/L), with AuNPs’ limit of detection (LoD) as 0.42 mg/L (wash-step), 0.87 mg/L (bridged structure) and AuNRs LoD as 0.35 mg/L. AuNRs are therefore more sensitive than AuNPs however the test line signal intensity suggests AuNPs are visually stronger. Furthermore, with the drawbacks of the bridged structure's complex fabrication and wash-step dipstick format's multi-steps, conventional LFIAs with AuNPs (89.5 μg/ml mAbs) conjugate in 10 min turnaround time were developed (LoD: 1.04 mg/L). Intra- assay CV% and inter- assay CV% are 13.69% 21.75%, accordingly. Human samples were then tested to address the matrix effect, with an average recovery rate of 99.37 ± 2.23% and an average CV% of 2.81%.

The presence and fate of antimicrobial residues in the environment is a subject of growing concern. Previous researchers have demonstrated the persistence of residues in soil and water. Additionally, antimicrobial resistance is a growing concern, particularly to public health, animal health and economic development. In this study, a low cost, commercial blood glucose meter was explored as the basis for detecting antimicrobial residues in conjunction with a microorganism sensitive to this residue. A microbial bioassay was developed based on the metabolic response of Geobacillus stearothermophilus, a sensitive bacteria used in the determination of antimicrobial residues in food products, by measuring changes in glucose as a result of metabolic activity. After optimizing experimental conditions, this sensing strategy was tested using bacterial cultures in the presence of colistin, a last-resort antibiotic used for human and animal health. Growth of G. stearothermophilus was measurable as a change in glucose concentration after 2–4 h incubation at 60 °C, when LB media was supplemented with 100 mg/dL of glucose. The lowest measured colistin concentration that resulted in inhibition of growth was 1 mg/L colistin and an increase in lag phase resulted at 100 µg/L colistin. To increase the sensitivity of the assay, we then added a sub-inhibitory concentration of chloramphenicol to the media and found that growth inhibition could be achieve at a lower colistin concentration of 8 µg /L. These results provide a promising basis for a future low-cost sensor to identify antimicrobial residues from environmental samples in the field.

Multiplex assays often rely on expensive sensors incorporating covalently linked fluorescent dyes. Herein, we developed a self-assembling aptamer-based multiplex assay. This multiplex approach utilizes a previously established split aptamer sensor in conjugation with a novel split aptamer sensor based upon a malachite green DNA aptamer. This system was capable of simultaneous fluorescent detection of two SARS COVID-19-related sequences in one sample with individual sensors that possesses a limit of detection (LOD) in the low nM range. Optimization of the Split Malachite Green (SMG) sensor yielded a minimized aptamer construct, Mini-MG, capable of inducing fluorescence of malachite green in both a DNA hairpin and sensor format.

The development of simple sensing platforms for evaluating the oral conditions has attracted great attentions for healthcare. Saliva or toothpaste contains various analytes that can indicate health conditions. A salivary glucose sensing platform can provide a convenient and non-invasive alternative detection approach for diabetic patients. Toothbrush is used every day, and it has an easy access to saliva biomarker and toothpaste residues. Here, we demonstrate for the first time an amperometric biosensor on a toothbrush, using glucose as a typical analyte. The carbon graphite ink and the Ag/AgCl ink are painted on a toothbrush as the sensing electrodes, followed by the enzyme immobilization. The sensor shows an excellent detection performance for glucose with a concentration ranging from 0.18 mM to 5.22 mM and a short detection time of less than 5 min. The sensor is promising for the non-invasive monitoring of salivary glucose levels in diabetic patients when they brush their teeth. We anticipate that these results would open up exciting opportunities for developing new toothbrush sensors, as well as advance related healthcare applications.

Triglycerides (TG) are an important biomarker of various diseases including hyper-lipidemia. Current emergent requirements for TG sensing include the development of electrochemical sensors for easy, cost-effective, disposable and single use triglyceride sensors. We propose a TG sensor using an engineered glycerol 3-phosphate oxidase (GlpO) and electrochemical detection. In this study, we aimed to develop an electrochemical TG sensor based on engineering the oxidative half reaction of GlpO to be oxygen insensitive, with the employment of an interdigitated electrode (IDE). To construct an oxygen insensitive mutant GlpO, we constructed a double mutant, Met104Phe/Asp169Glu, which revealed an engineered GlpO exhibiting repressed oxidase activity, while its dye-mediated dehydrogenase activity enhanced. The electrochemical enzyme sensor was constructed for the measurement of TG based on engineered GlpO using disposable screen-printed carbon electrode (SPCE) or disposable IDE using Ru complex as the electron mediator. By using the disposable IDE sensor, a highly sensitive electrochemical sensor for Glp was achieved, with the sensitivity of 0.4 µA/mM. The improved sensitivity was 2.4 times higher than that of SPCE (0.17 µA/mM), with LOD of 0.022 mM. Furthermore, the dry sensor strip, where the double mutant GlpO and Ru complex were dropcasted and dried on the IDE, was prepared and the Glp concentration was successfully measured in the delipidized serum solution. Therefore, by the employment of the established pretreatment method for TG to release Glp, a highly sensitive, accurate, easy and rapid electrochemical measurement method for TG will be developed using constructed M104F/D169E mutant GlpO with the combination of IDE.

Recently, significant efforts have been made to develop prostheses, soft rehabilitation, and assistive devices that enhance the quality of life of limb amputees and the activities of daily living (ADL) of stroke patients. Therefore, this present study provides a general overview of the current prosthetic, assistive, and rehabilitative devices with a focus on actuators that provide actuation via shape-memory alloys (SMA). Shape-memory alloy (SMA)-based actuators are the subject of considerable research as they possess high force-to-weight ratio, quiet operation, muscular mobility, bio-compatibility, and accessible design options, all of which can potentially be used to develop inventive actuating systems. Several studies have examined the use of SMA-actuated devices in the medical and engineering industry. They have also, more recently, been used to develop soft robotic systems. This present review primarily focuses on the characterization, number, type of actuator, degrees of freedom (DOF), weight, cooling technique, control strategies, and applications as well as the advantages and disadvantages of plate, spring, and wire-based SMA actuators. Composite-based upper limb SMA actuators were also reviewed and compared in terms of the matrix, reinforcing materials, SMA configuration actuator dimensions, and manufacturing method as well as their advantages and disadvantages. The findings indicate that, in the last few years, more studies have examined developing novel intelligent materials with which to improve hand flexibility. Therefore, SMA materials have a promising future in the development of intelligent designs for hand-robots. They may also be used to improve control robustness as well as the accuracy of hand functions for ADL and effective rehabilitation.

Developing efficient monitoring systems to control reinforced concrete structures (RCS) is still an open research line in the building sector. Thus, in this work was proposed the novelty use of Ni voltammetric sensor to control the concrete conditions by means of PCA model. The efficiency of voltammetric sensors are verified in other sectors like food or wastewater treatment, where the sensors are used in liquid media, in the study was intended verify the high potential use of this sensors in porous materials such as concrete. With this purpouse the sensor response was characterized in three different concretes (w/c = 0.6, w/c = 0.5 and w/c = 0.4) and three different concrete conditions (water satured conditions, presence of chlorides and concrete carbonation). Then, was developed a PCA model, where was verified the capability of the sensor to classify the concrete state. The validation of the model pointed an acceptance range between 78.3% and 95.4% (with a 95% confidence index).

Abstract not available

Nanocrystalline ZnO quantum dots (QD) with a diameter of 10 nm was synthesized and tested toward eight different toxic industrial chemicals (i.e., nitrogen dioxide (NO2), hydrogen sulfide (H2S), ammonia (NH3), carbon monoxide (CO), methane (CH4), ethanol (C2H5OH), acetone (CH3)2CO, and toluene (C6H5CH3)) with a broad concentration range at five different operating temperatures. Systemic studies allow to determine the kinetics of gas sensing as well as the competing reactions of analytes with sensing material and adsorbed oxygen. ZnO QD showed an excellent sensing performance toward NO2 and H2S in comparison to other target analytes. The selectivity can be further improved by controlling the operating temperature (i.e., higher selectivity toward NO2 and H2S were achieved at 300 °C and 450 °C, respectively). Moreover, the optimal temperature was found to be analyte dependent.

Enhancing the stability and sensitivity of electrochemical biosensors is highly significant for their practical application. Herein, inspired by the formation of mussel foot protein, we proposed a strategy to construct a hemoglobin-based biosensor for hydrogen peroxide detection using a hydrophobic ionic liquid (HIL) coordination assisted microfluidic technology. The active layer HIL@Hb was achieved by mixing BBimPF6 (HIL) and Hb via a microfluidic channel, in which HIL helps to maintain the conformational dynamic mobility of hemoglobin (Hb), while the coordination process in a microfluidic reactor prevents aggregation of Hb. Further, the electrode surface was modified with ultra-thin MXene-Ti3C2 nanosheets to ensure the effective adhesion of active layer and collection of sensing signals, thus improving the sensitivity of the sensor by synergistic catalysis. Experimental results demonstrate that our designed sensor has good repeatability and stability, which can retain 93% of the initial current response after 30 uses and about 90.11% of its primary current response to H2O2 after 30 days. And it has a good linear response range of 1.996–27.232 μM, detection limit reaching 1.996 nM (signal-to-noise ratio, S/N = 3), sensitivity of 52.08 μA·μM−1·cm−2. Overall, this research offers a facile and effective strategy for constructing a stable biosensor to effectively detect hydrogen peroxide.