mM-1 Cm-2 Research Articles

Seamless integration of a nickel-based metal-organic framework with three-dimensional substrates for nonenzymatic glucose sensing.

The effective integration of nanomaterials with underlying current collectors is a key factor affecting the performance of nonenzymatic glucose sensors, where an inappropriate integration structure often leads to poor electron transport and instability. In this work, a seamless integrated electrode was constructed by the in situ immobilizing of a nickel-based metal-organic framework (Ni-MOF) on a three-dimensional (3D) conductive nickel foam (NF) for highly sensitive and durable glucose sensing. Facilitated by a rapid microwave-assisted reaction, a robust interfacial interaction between the Ni-MOF and the substrate was established through in situ conversion from nickel oxide (NiO). The fabricated Ni-MOF/NF electrode exhibits an excellent limit of detection (LOD) of 2.65 μM and an impressive sensitivity (14.31 mA cm-2 mM-1) within the linear range (4-576 μM), which is significantly boosted compared with that of an electrode prepared by a typical drop-casting method (3.56 mA cm-2 mM-1 in 4-1836 μM). Characterization and electrochemical tests reveal that this integrated structure on the one hand contributes to fast electron transport and thus has enhanced sensitivity and on the other hand leads to exceptional durability with its structural integrity maintained under bending, shaking, and ultrasonication. Moreover, this seamless integration method was also employed to immobilize the Ni-MOF converted from the pre-chemically deposited NiO layer on another type of substrate, 3D carbon paper (CP), demonstrating the versatility of this facile strategy in creating diverse electrochemical electrodes for applications beyond glucose sensing.

Sensitive Cr3+ sensor based on novel poly(luminol-co-1,8-diaminonaphthalene)/CeO2/MWCNTs nanocomposites.

In this study, poly(luminol-co-1,8-diaminonaphthalene) (PLim-DAN) was synthesized and subsequently modified with MWCNTs and CeO2 NPs. The synthesized nanocomposites were analyzed using IR, SEM, TEM, and XRD. Furthermore, a comprehensive set of thermal behavior measurements were taken using TGA/DTG analysis. Next, the electroactivity of the developed nanocomposites was tested as an electrochemical sensor to measure the concentration of Cr3+ ions in phosphate buffers. The GCE adapted with the PLim-DAN/CeO2/CNTs-10% nanocomposite (NC) exhibited the highest current response among the other compositions and copolymers. The fabricated nanocomposite sensor showed high sensitivity, with a value of 19.78 μA μM-1 cm-2, and a low detection limit of 4.80 ± 0.24 pM. The analytical performance was evaluated by plotting a current calibration curve versus the concentration of Cr3+ ions. It was found to be linear (R2 = 0.9908) over the range of 0.1 nM to 0.1 mM, identified as the linear dynamic range (LDR). This electrochemical sensor demonstrated that it could be a useful tool for environmental monitoring by accurately detecting and measuring carcinogenic Cr3+ ions in real-world samples.

An MXene-supported cobalt-MOF nanocomposite-printed electrochemical sensor with high sensitivity for blood creatinine detection in point-of-care settings.

2D MXenes have been used as electrochemical sensor materials, but their output current signal remains weak in point of care (PoC) settings. To address this issue, here we report a novel MXene-supported cobalt-MOF-based nanocomposite, which is used with a carbon black (CB) ink and 3-D printed as the CoMOF-MXene@CB layered electrode structure for the development of a sensor electrode and a PoC chip for electrochemical detection of blood creatinine with an enhanced current range, specificity, and sensitivity. The limit of detection (LOD) and sensitivity of the fabricated sensor were found to be 0.005 μM and 1.1 μA μM-1 cm-2, which are 44 times lower and 32 times enhanced, respectively, as compared to the existing literature report (LOD 0.22 μM and sensitivity 0.034 μA μM-1) for creatinine sensing in PoC settings. The sensor exhibited an excellent linear sensor response ranging from 10 to 800 μM and good reproducibility, stability, and selectivity with significant accuracy. These characteristics helped the sensor to accurately determine the creatinine levels in real human serum samples.

The enhanced electrocatalytic performance of nanoscopic Cu6Pd12Fe12 heterometallic molecular box encaged cytochrome c.

Designing molecular cages for atomic/molecular scale guests is a special art used by material chemists to harvest the virtues of the otherwise vile idea known as "the cage". In recent years, there has been a notable surge in research investigations focused on the exploration and utilization of the distinct advantages offered by this art in the advancement of efficient and stable bio-electrocatalysts. This usually is achieved through encapsulation of biologically accessible redox proteins within specifically designed molecular cages and matrices. Herein, we present the first successful method for encaging cytochrome c (Cyt-c), a clinically significant enzyme system, inside coordination-driven self-assembled Cu6Pd12Fe12 heterometallic hexagonal molecular boxes (Cu-HMHMB), in order to create a Cyt-c@Cu-HMHMB composite. 1H NMR, FTIR, and UV-Vis spectroscopy, ICP-MS, TGA and voltammetric investigations carried out on the so-crafted Cyt-c@Cu-HMHMB bio-inorganic composite imply that the presented strategy ensures encaging of Cyt-c in a catalytically active, electrochemically stable and redox-accessible state inside the Cu-HMHMB. Cyt-c@Cu-HMHMB is demonstrated to exhibit excellent stability and electrocatalytic activity toward very selective, sensitive electrochemical sensing of nitrite exhibiting a limit of detection as low as 32 nanomolar and a sensitivity of 7.28 μA μM-1 cm-2. Importantly, Cyt-c@Cu-HMHMB is demonstrated to exhibit an excellent electrocatalytic performance toward the 4ē pathway oxygen reduction reaction (ORR) with an onset potential of 0.322 V (vs. RHE) and a Tafel slope of 266 mV dec-1. Our findings demonstrate that Cu-HMHMB is an excellent matrix for Cyt-c encapsulation. We anticipate that the entrapment-based technique described here will be applicable to other enzyme systems and Cyt-c for various electrochemical and other applications.

Tailoring cellulose paper via electroless CuSnB deposition for selective electrochemical detection of dopamine.

A novel, biodegradable substrate based, and cost-effective flexible electrochemical sensor was developed for the highly selective and sensitive detection of one of the major neurotransmitters, dopamine, which can be utilised as a disposable electrode for point-of-care diagnostic applications. The active material CuSnB decorated over cellulose paper exhibits good sensitivities of 3.92 μA μM-1 cm-2 with a limit of detection of 0.5 nM. Moreover, the flexible sensor demonstrated superior selectivity towards co-existing metabolites such as ascorbic acid, glucose, and uric acid, in addition to stability at various mechanical deformations.

An on-site and portable electrochemical sensing platform based on spinel zinc ferrite nanoparticles for the quality control of paracetamol in pharmaceutical samples.

In this study, crystalline spinel zinc ferrite nanoparticles (ZnFe2O4 NPs) were successfully prepared and proposed as a high-performance electrode material for the construction of an electrochemical sensing platform for the detection of paracetamol (PCM). By modifying a screen-printed carbon electrode (SPE) with ZnFe2O4 NPs, the electrochemical characteristics of the ZnFe2O4/SPE and the electrochemical oxidation of PCM were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and differential pulse voltammetry (DPV) methods. The calculated electrochemical kinetic parameters from these techniques including electrochemically active surface area (ECSA), peak-to-peak separation (ΔEp), charge transfer resistance (Rct), standard heterogeneous electron-transfer rate constants (k0), electron transfer coefficient (α), catalytic rate constant (kcat), adsorption capacity (Γ), and diffusion coefficient (D) proved that the as-synthesized ZnFe2O4 NPs have rapid electron/mass transfer characteristics, intrinsic electrocatalytic activity, and facilitate the adsorption-diffusion of PCM molecules towards the modified electrode surface. As expected, the ZnFe2O4/SPE offered excellent analytical performance towards sensing of PCM with a detection limit of 0.29 μM, a wide linear range of 0.5-400 μM, and high electrochemical sensitivity of 1.1 μA μM-1 cm-2. Moreover, the proposed ZnFe2O4-based electrochemical nanosensor also exhibited good repeatability, high anti-interference ability, and practical feasibility toward PCM sensing in a pharmaceutical tablet. Based on these observations, the designed electrochemical platform not only provides a high-performance nanosensor for the rapid and highly efficient detection of PCM but also opens a new avenue for routine quality control analysis of pharmaceutical formulations.

Nanomolar level electrochemical detection of glycine on a miniaturized modified screen-printed carbon-based electrode: a comparison of performance with glassy carbon electrode system.

In this work, we demonstrate the electrochemical (EC) sensing of glycine (GLY) on a gold-copper nanocluster on nitrogen-doped graphene quantum dot-modified (indigenously fabricated) screen-printed electrode (AuCuNC@N-GQD/SPE). SPE was fabricated by step-by-step printing of reference, working, and counter electrodes to develop an all-printed SPE. A comparison strategy between SPE and the glassy carbon electrode (GCE) towards the EC sensing of GLY was carried out. The sensing performance was enhanced while replacing GCE with SPE. The limit of detection (LOD) for GLY obtained by EC sensing with AuCuNC@N-GQD/GCE was 10 nM and that with AuCuNC@N-GQD/SPE was 10 times lower, 1 nM, and is the lowest LOD value reported hitherto. Compared with AuCuNC@N-GQD/GCE, the current response of AuCuNC@N-GQD/SPE exhibited a ∼2.6-times enhancement with a sensitivity of 0.206 μA μM-1 cm-2. Thus, the successful shift from GCE to SPE not only miniaturizes the sensor device but also enhances the electrochemical detection performance.

Surface engineering of carbon microspheres with nanoceria wrapped on MWCNTs: a dual electrocatalyst for simultaneous monitoring of molnupiravir and paracetamol.

In the present study, nanoceria-decorated MWCNTs (CeNPs@MWCNTs) were synthesized using a simple and inexpensive process. Molnupiravir (MPV) has gained considerable attention in recent years due to the infection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Since some people infected with COVID-19 experience fever and headaches, paracetamol (PCM) has been prescribed to relieve these symptoms. Therefore, there is an urgent need to monitor and detect these drugs simultaneously in pharmaceutical and biological samples. In this regard, we developed a novel sensor based on nanoceria-loaded MWCNTs (CeNPs@MWCNTs) for simultaneous monitoring of MPV and PCM. The incorporation of CeNPs@MWCNTs electrocatalyst into a glassy carbon microsphere fluorolube oil paste electrode (GCMFE) creates more active sites, which increase the surface area, electrocatalytic ability, and electron transfer efficiency. Interestingly, CeNPs@MWCNTs modified GCMFE demonstrated excellent detection limits (6.0 nM, 8.6 nM), linear ranges (5.0-5120 nM, 8.0-4162 nM), and sensitivities (78.6, 94.3 μA μM-1 cm-2) for simultaneous detection of MPV and PCM. The developed CeNPs@MWCNTs electrocatalyst modified GCMFE exhibited good repeatability, anti-interference capability, stability, and real-time analysis with good recovery results, which clearly indicates that it can be used for real-time industrial applications.

Urchin-like CoP3/Cu3P heterostructured nanorods supported on a 3D porous copper foam for high-performance non-enzymatic electrochemical dopamine sensors.

In this study, we developed a high-performance non-enzymatic electrochemical sensor based on urchin-like CoP3/Cu3P heterostructured nanorods supported on a three-dimensional porous copper foam, namely, CoP3/Cu3P NRs/CF, for the detection of dopamine. Benefiting from the promising intrinsic catalytic activities of CoP3 and Cu3P, urchin-like microsphere structures, and a large electrochemically active surface area for exposing numerous accessible catalytic active sites, the proposed CoP3/Cu3P NRs/CF shows extraordinary electrochemical response towards the electrocatalytic oxidation of dopamine. As a result, the CoP3/Cu3P NRs/CF sensing electrode has a broad detection window (from 0.2 to 2000 μM), low detection limit (0.51 μM), high electrochemical sensitivity (0.0105 mA μM-1 cm-2), excellent selectivity towards dopamine in the coexistence of some interfering species, and good stability for dopamine determination. More importantly, the CoP3/Cu3P NRs/CF catalyst also exhibits excellent catalytic activity, sensitivity, and selectivity for dopamine detection under simulated human body conditions at a physiological pH of 7.25 (0.1 M PBS) at 36.6 °C.

Development of an efficient electrochemical sensing platform based on ter-poly(luminol-o-anisidine-o-toluidine)/ZnO/GNPs nanocomposites for the detection of antimony (Sb3+) ions.

A poly(luminol-o-anisidine-o-toluidine) terpolymer was synthesized, characterized, and modified with GNPs and ZnO NPs. The nanocomposites were then examined for their electroactivity and potential use as cationic electrochemical sensors for detecting Sb3+ ions in phosphate buffer on the surface of a glassy carbon electrode (GCE). Among the different compositions and the terpolymer, the GCE adapted with the PLAT/ZnO/GNPs-5% nanocomposite displayed the highest current response. The fabricated nanocomposite sensor exhibited high sensitivity, with a value of 21.4177 μA μM-1 cm-2, and a low detection limit of 95.42 pM. The analytical performance of the sensor was evaluated over the linear dynamic range (LDR) of 0.1 nM to 0.01 mM. The proposed sensor is effective in detecting and measuring carcinogenic Sb3+ ions in real environmental samples using an electrochemical approach, making it a promising tool for environmental monitoring.

Screen printed 3D microfluidic paper-based and modifier-free electroanalytical device for clozapine sensing.

The increasing demand in healthcare for accessible and cost-effective analytical tools is driving the development of reliable platforms to the customization of therapy according to individual patient drug serum levels, e.g. of anti-psychotics in schizophrenia. A modifier-free microfluidic paper-based electroanalytical device (μPED) holds promise as a portable, sensitive, and affordable solution. While many studies focus on the working electrode catalysts, improvements by engineering aspects e.g. of the electrode arrangement are less reported. In our study, we demonstrate the enhanced capabilities of the 3D electrode layout of μPED compared to 2D μPED arrangements. We especially show that screen printing can be employed to prepare 3D μPEDs. We conducted a comparison of different 2D and 3D electrode arrangements utilizing cyclic voltammetry in [Fe(CN)6]3-/4-, along with square-wave voltammetry for clozapine (CLZ) sensing. Our findings reveal that the utilization of the 3D μPED leads to an increase in both the electrochemically active surface area and the electron transfer rate. Consequently, this enhancement contributes to improve sensitivity in the CLZ sensing. The 3D μPED clearly outperforms the 2D μPED arrangement in terms of signal strength. With the 3D μPED under the optimized conditions, a linear dose-response for a concentration range from 7.0 to 100 μM was achieved. The limit of detection and sensitivity was determined to be 1.47 μM and 1.69 μA μM-1 cm-2, respectively. This evaluation is conducted in the context of detection and determination of CLZ in a human blood serum sample. These findings underscore the potential of the 3D μPED for future applications in pharmacokinetic analyses and clinical tests to personalize the management of schizophrenia.

Design and fabrication of La-based perovskites incorporated with functionalized carbon nanofibers for the electrochemical detection of roxarsone in water and food samples.

The pentavalent arsenic compound roxarsone (RSN) is used as a feed additive in poultry for rapid growth, eventually ending up in poultry litter. Poultry litter contains chicken manure, which plays a vital role as an affordable fertilizer by providing rich nutrients to agricultural land. Consequently, the extensive use of poultry droppings serves as a conduit for the spread of toxic forms of arsenic in the soil and surface water. RSN can be easily oxidized to release highly carcinogenic As(III) and As(IV) species. Thus, investigations were conducted for the sensitive detection of RSN electrochemically by developing a sensor material based on lanthanum manganese oxide (LMO) and functionalized carbon nanofibers (f-CNFs). The successfully synthesised LMO/f-CNF composite was confirmed by chemical, compositional, and morphological studies. The electrochemical activity of the prepared composite material was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results confirmed that LMO/f-CNF showed enhanced electrocatalytic activity and improved current response with a good linear range (0.01-0.78 μM and 2.08-497 μM, respectively), exhibiting a low limit of detection (LOD) of 0.004 μM with a high sensitivity of 13.24 μA μM-1 cm-2 towards the detection of RSN. The noteworthy features of LMO/f-CNF composite with its superior electrochemical performance enabled reliable reproducibility, exceptional stability and reliable practical application in the analysis of tap water and food sample, affording a recovery range of 86.1-98.87%.

Sustainable design of high-performance multifunctional carbon electrodes by one-step laser carbonization for supercapacitors and dopamine sensors.

Laser carbonization is a rapid method to produce functional carbon materials for electronic devices, but many typical carbon precursors are not sustainable and/or require extensive processing for electrochemical applications. Here, a sustainable concept to fabricate laser patterned carbon (LP-C) electrodes from biomass-derived sodium lignosulfonate, an abundant waste product from the paper industry is presented. By introducing an adhesive polymer interlayer between the sodium lignosulfonate and a graphite foil current collector, stable, abrasion-resistant LP-C electrodes can be fabricated in a single laser irradiation step. The electrode properties can be systematically tuned by controlling the laser processing parameters. The optimized LP-C electrodes demonstrate a promising performance in supercapacitors and electrochemical dopamine biosensors. They exhibit high areal capacitances of 38.9 mF cm-2 in 1 M H2SO4 and high energy and power densities of 4.3 μW h cm-2 and 16 mW cm-2 in 17 M NaClO4, showing the best performance among biomass-derived LP-C materials reported so far. After 20 000 charge/discharge cycles, they retain a high capacitance of 81%. Dopamine was linearly detected in the range of 0.1 to 20 μM with an extrapolated limit of detection of 0.5 μM (S/N = 3) and high sensitivity (13.38 μA μM-1 cm-2), demonstrating better performance than previously reported biomass-derived LP-C dopamine sensors.

Ni@TiO2 nanoribbon array electrode for high-efficiency non-enzymatic glucose biosensing.

The exploration of noble metal-free nanoarrays as high-activity catalytic electrodes for glucose biosensing holds great significance. Herein, we propose a Ni nanoparticle-decorated TiO2 nanoribbon array on a titanium plate (Ni@TiO2/TP) as an effective non-enzymatic glucose biosensing electrode. The as-prepared Ni@TiO2/TP electrode demonstrates rapid glucose response, a wide linear response range (1 μM to 1 mM), a low detection limit (0.08 μM, S/N = 3), and high sensitivity (10 060 and 3940 μA mM-1 cm-2), with good mechanical flexibility and stability. Moreover, it proves efficient in glucose biosensing in real human blood serum and cell culture fluid. Thus, it is highly promising for practical applications.

High performance nonenzymatic electrochemical sensors via thermally grown Cu native oxides (CuNOx) towards sweat glucose monitoring.

Diabetes, which is the seventh leading cause of death globally, necessitates real-time blood glucose monitoring, a process that is often invasive. A promising alternative is sweat glucose monitoring, which typically uses transition metals and their oxide nanomaterials as sensors. Despite their excellent surface-to-volume ratio, these materials have some drawbacks, including poor conductivity, structural collapse, and aggregation. As a result, selecting highly electroconductive materials and optimizing their nanostructures is critical. In this work, we developed a high-performance, low-cost, nonenzymatic sensor for sweat glucose detection, using the thermally grown native oxide of copper (CuNOx). By heating Cu foil at 160, 250, and 280 °C, we grew a native oxide layer of approximately 140 nm cupric oxide (CuO), which is excellent for glucose electrocatalysis. Using cyclic voltammetry, we found that our CuNOx sensors prepared at 280 °C exhibited a sensitivity of 1795 μA mM-1 cm-2, a linear range up to the desired limit of 1.00 mM for sweat glucose with excellent linearity (R2 = 0.9844), and a lower limit of detection of 135.39 μM. For glucose sensing, the redox couple Cu(II)/Cu(III) oxidizes glucose to gluconolactone and subsequently to gluconic acid, producing an oxidation current in an alkaline environment. Our sensors showed excellent repeatability and stability (remaining stable for over a year) with a relative standard deviation (RSD) of 2.48% and 4.17%, respectively, for 1 mM glucose. The selectivity, when tested with common interferants found in human sweat and blood, showed an RSD of 4.32%. We hope that the electrocatalytic efficacy of the thermally grown CuNOx sensors for glucose sensing can introduce new avenues in the fabrication of sweat glucose sensors.

Facile preparation of a CoNiS/CF electrode by SILAR for a high sensitivity non-enzymatic glucose sensor.

The nanomaterials for non-enzymatic electrochemical sensors are usually pre-synthesized and coated onto electrodes by ex situ methods. In this work, amorphous cobalt-nickel sulfide (CoNiS) nanoparticles were facilely prepared on copper foam (CF) by the in situ successive ionic layer adsorption and reaction (SILAR) method, and as-prepared CoNiS/CF was studied as an electrode for non-enzymatic glucose sensing. It was analyzed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). This binary sulfide electrode showed better performance toward glucose oxidation compared to the corresponding single sulfide and showed a wide linear range of 0.005 to 3.47 mM, a high sensitivity of 2298.7 μA mM-1 cm-2 and a low detection limit of 2.0 μM. The sensor exhibited high sensitivity and good repeatability and stability and was able to detect glucose in an actual sample. This work provides a simple and fast in situ electrode preparation method for a high-sensitivity glucose sensor.

Green synthesized gold nanoparticles and CuO-based nonenzymatic sensor for saliva glucose monitoring.

Glucose, essential for brain and muscle functions, requires careful monitoring in diabetes and other chronic disease management. While blood glucose monitoring provides precise information about these diseases, it remains an invasive method. Saliva glucose monitoring could offer an alternative approach, but the glucose concentration in saliva is very low. In this work, we report a simple, low-cost, highly sensitive nonenzymatic electrochemical glucose sensor. We developed this sensor using green synthesized gold nanoparticles (AuNPs) and wet chemical synthesized copper oxide (CuO) nanoparticles on a screen-printed carbon electrode (Au/CuO/SPCE). The sensor's high sensitivity results from dual amplification strategies using AuNPs and CuO nanomaterials, each demonstrating catalytic activity towards glucose. This shows promising potential for saliva glucose monitoring. The AuNPs were synthesized using an Au precursor and orange peel extract (OPE), yielding stable colloidal AuNPs with a mean diameter of about 37 nm, thus eliminating the need for additional capping agents. Under optimal conditions, amperometric tests revealed that the sensor responded linearly to glucose concentrations ranging from 2 μM to 397 μM with a sensitivity of 236.70 μA mM-1 cm-2. Furthermore, the sensor demonstrated excellent reproducibility, stability and high selectivity for glucose in the presence of different biomolecules. We validated the sensor's efficacy by measuring glucose in human saliva, showing its potential for noninvasive glucose monitoring. This research advances the development of point-of-care devices, positioning the sensor as a promising tool for noninvasive glucose monitoring and improved diabetes management.

In situ growth of self-supported CuO nanorods from Cu-MOFs for glucose sensing and elucidation of the sensing mechanism.

Herein, we present a simple and mild method to in situ prepare CuO nanostructures for non-enzymatic glucose sensing. A Cu-metal organic framework (Cu-MOF) precursor was first directly grown on a pencil lead electrode with 3D graphene-like surfaces (EPLE) and then in situ transformed into CuO nanorods. The CuO nanorod-modified EPLE (CuO/EPLE) shows high sensitivity (1138.32 μA mM-1 cm-2), fast response time (1.5 s) and low detection limit (0.11 μM) for glucose oxidation. It has been found that NaOH promoted the generation of ˙OH groups and Cu(III) on the CuO surface, which then facilitated the electrochemical oxidation of glucose. Signals characteristic of hydroxyl and carbon-centered radical adducts were detected by EPR. Furthermore, the CuO/EPLE sensor also shows good accuracy in glucose determination in human serum samples.

Multi-MXene assisted large-scale manufacturing of electrochemical biosensors based on enzyme-nanoflower enhanced electrodes for the detection of H2O2 secreted from live cancer cells.

In situ monitoring of H2O2 in cellular microenvironments plays a critical role in the early diagnosis and pretreatment of cancer, but is limited by the lack of efficient and low-cost strategies for the large-scale preparation of real-time biosensors. Herein, a universal strategy for MXene-based composite inks combined with a scalable screen-printing process is validated in large-scale manufacturing of electrochemical biosensors for in situ detection of H2O2 secreted from live cells. Compositing biocompatible carboxymethyl cellulose (CMCS) with excellent conductive MXene, a water-based ink electrode (MXene/CMCS) with tunable viscosity is efficiently printed with desirable printing accuracy. Subsequently, the MXene/CMCS@HRP electrochemical biosensor exhibits stable electrochemical performance through HRP nanoflower modification, showing rapid electron transport and high electrocatalytic capacity, and demonstrating a low limit of detection (0.29 μM) with a wide linear detection range (0.5 μM-3 mM), superior sensitivity (56.45 μA mM-1 cm-2), long-term stability and high anti-interference ability. Moreover, this electrochemical biosensor is effectively employed for in situ detection of H2O2 secreted from HeLa cells, revealing good biocompatibility and outstanding biosensing capability. This proposed strategy not only extends the possibility of low-cost biomedical devices, but also provides a promising approach for early diagnosis and treatment of cancer.

In situ generation of turbostratic nickel hydroxide as a nanozyme for salivary glucose sensor.

Among the 3d-transition metal hydroxide series, nickel hydroxide is a well-studied electroactive catalyst. In particular, nickel hydroxide and its composite materials are well-suited for non-enzymatic glucose sensing. The electrocatalytic efficiency of nickel hydroxide is attributed to the thickness or to be precise, the thinness of the electroactive layer. Herein, we have successfully prepared metallic nickel@nickel hydroxide nanosheets through a straightforward one-pot solvothermal method. We were able to electrochemically generate a highly sensitive α-Ni(OH)2 on the nanosheets. The dynamic generation and synergy between α- and β-Ni(OH)2, imparts a glucose oxidase enzyme-like ability to the catalyst. Our proposed nickel nanozyme exhibits a good sensitivity of 683 μA mM-1 cm-2 for glucose. The sensor operates in the range of 0.001-3.1 mM, with a lower limit of detection (LOD) of 9.1 μM and exhibits a response time of ≈00.1 s. Nickel-nanozyme demonstrated better selectivity for glucose in the presence of interfering compounds. Notably, the sensor does not suffer from an interfering oxygen evolution reaction. This greatly improves sensitivity in glucose detection in lower concentrations making the sensor viable to measure salivary glucose levels. In this study, we demonstrate that our sensor can detect glucose in human saliva. The real sample analysis was carried out with saliva samples from three healthy human volunteers and one prediabetic volunteer. Our proposed sensor measurements show excellent agreement with calculated salivary glucose levels with 98% accuracy in sensing glucose in real saliva samples.