Multifunctional Nickel Phosphate Nano/Microflakes 3D Electrode for Electrochemical Energy Storage, Nonenzymatic Glucose, and Sweat pH Sensors

Formamide-assisted synthesis of phosphate-intercalated Ni(OH)2/NiOOH electrode for boosting oxygen evolution reaction

Electrochemical water splitting (EWS) represents a promising method for green hydrogen production. However, the commercial viability of this approach is significantly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Layered Ni(OH)2/NiOOH serves as a low-cost and effective OER electrocatalyst, yet the activity and stability do not meet the requirements for commercial EWS, particularly in terms of operational stability under high current densities. Herein, we report a phosphate-intercalated (Pi) Ni(OH)2/NiOOH synthesized with the assistance of formamide (FA), termed NiOH-Pi-FA, which demonstrates significantly-enhanced OER performance. Systematic investigations reveal that FA facilitates phosphate intercalation, which improves OER via lattice oxygen oxidation, interlayer proton transport, electrode conductivity, electrode surface wetting and O2 bubbles release. More importantly, FA alters the catalyst's morphology, creating a porous structure and reducing catalyst particle size, which decreases the interlayer proton transport distance. FA also increases the surface roughness, promoting the release of O2 bubbles. Consequently, the OER performance of NiOH-Pi-FA is much better than that of Ni(OH)2/NiOOH prepared without FA (NiOH-Pi). It achieves overpotentials of 106 and 223 mV at current densities of 10 and 100 mA cm-2, respectively, and maintains exceptional stability at 350-330 mA cm-2 for over 400 h. Overall, the OER performance of NiOH-Pi-FA surpasses that of RuO2 and other Ni-based hydroxide electrocatalysts, offering valuable insights for designing efficient and stable OER catalysts.

New trends in potentiometric sensors: From design to clinical and biomedical applications

Potentiometry, a well-established electrochemical technique, provides a powerful and versatile method for the sensitive and selective measurement of a variety of analytes by measuring the potential difference between two electrodes, allowing for a direct and rapid readout of ion concentrations. This makes it a valuable tool in a variety of applications including industry, agriculture, forensics, medical, environmental assessment, and pharmaceutical drug analysis, therefore it has received significant attention from the scientific community. Their broad implementation in sensing applications arises through their many benefits, including ease of design, fabrication, and modification; rapid response time; high selectivity; suitability for use with colored and/or turbid solutions; and potential for integration into embedded systems interfaces. Owing to these advantages and diverse applicability, sustained research and development in the field has resulted in the emergence of several notable trends in the field. 3D printing is the most recent technique used in potentiometry which offers many benefits such as improved flexibility and precision in the manufacturing of ion-selective electrodes and rapid prototyping decreases the time needed during optimization of important electrochemical parameters. Additionally, paper-based sensors are cost-effective and versatile platforms for in-field (point-of-care, POC) analysis, permitting rapid determination of a variety of analytes. One of the most interesting applications of potentiometry are wearable sensors which allow for the continuous monitoring of biomarkers, electrolytes and even pharmaceuticals, especially those with a narrow therapeutic index. Herein this review, we discuss several recent trends in potentiometric sensors since 2010, including 3D printing, paper-based devices, and other emerging techniques and the translation of potentiometric systems to wearable devices for the determination of ionic species or pharmaceuticals in biological fluids paving the way to various clinical and biomedical uses.

Unleashing the Full Potential of Electrochromic Heterostructured Nickel-Cobalt Phosphate for Optically Active High-Performance Asymmetric Quasi-Solid-State Supercapacitor Devices

The rational design of hybrid systems that combine capacitor and battery merits is crucial to enable the fabrication of high energy and power density devices. However, the development of such systems remains a significant barrier to overcome. Herein, we report the design of a Ni-Co phosphate (Ni3-xCox(PO4)2·8H2O) nanoplatelet-based system via a facile coprecipitation method at ambient conditions. The nanoplatelets exhibit multicomponent synergy, exceptional charge storage capabilities, rich redox active sites (ameliorating the redox reaction activity), and high ionic diffusion rate/electron transfer kinetics. The designed Ni3-xCox(PO4)2·8H2O offered a respectable gravimetric specific capacity and marvelous capability rate (966 and 595 C g-1 at 1 and 15 A g-1) over the Ni3(PO4)2·8H2O (327.3 C g-1) and Co3(PO4)2·8H2O (68 C g-1) counterparts. Additionally, the nanoplatelets showed enhanced photoactive storage performance with a 9.7% increase in the recorded photocurrent density. Upon integration of Ni3-xCox(PO4)2·8H2O as a positive pole and commercial activated carbon as a negative pole, the constructed hybrid supercapacitor device with PVA@KOH quasi-gel electrolyte exhibits great energy and power densities of 77.7 Wh kg-1 and 15998.54 W kg-1 with remarkable cycling stability of 6000 charging/discharging cycles and prominent Coulombic efficiency of 100%. Interestingly, two assembled devices are capable of glowing a red LED bulb for nearly 180 s. This research paves the way to design and fabricate electroactive species via a facile approach for boosting the design of a plethora of supercapattery devices.

Moving towards in pouch diagnostics for ostomy patients: exploiting the versatility of laser induced graphene sensors

The development of a 3D printed sensor for direct incorporation within stoma pouches is described. Laser induced graphene scribed on either side of polyimide film served as the basis of a 2 electrode configuration that could be integrated within a disposable pouch sensor for the periodic monitoring of ileostomy fluid pH. The graphene sensors were characterised using electron microscopy, Raman spectroscopy, DekTak profilometry with the electrochemical properties investigated using both cyclic and square wave voltammetry. Adsorbed riboflavin was employed as a biocompatible redox probe for the voltammetric measurement of pH. The variation in peak position with pH was found to be linear over pH 3-8 with a sub Nernstian response (43 mV/pH). The adsorbed probe was found to be reversible and exhibited minimal leaching through repeated scanning. The performance of the system was assessed in a heterogeneous bacterial fermentation mixture simulating ileostomy fluid with the pH recorded before and after 96 h incubation. The peak profile in the bacterial medium provided an unambiguous signal free from interference with the calculated pH before and after incubation (pH 5.3 to 3.66) in good agreement with that obtained with commercial pH probes.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10853-023-08881-x.

UiO-66-Derived PBA Composite as Multifunctional Electrochemical Non-Enzymatic Sensor Realizing High-Performance Detection of Hydrogen Peroxide and Glucose

In this work, a highly efficient multifunctional non-enzymatic electrochemical sensor is successfully fabricated based on a facile two-step synthetic strategy. It resolves two important challenges of poor stability and low reproducibility compared to conventional electrochemical enzyme-based sensors. Herein, a metal-organic framework (UiO-66) is selected as a sacrificial template to construct the corresponding Prussian blue analogue (PBA) target to improve its stability and conductivity, namely, PBA/UiO-66/NF. Target PBA/UiO-66/NF exhibits excellent electrochemical sensing performance as hydrogen peroxide (H₂O₂) and glucose sensors with ultrahigh sensitivity of up to 1903 μA mM^-1 cm^-2 for H₂O₂ and 22,800 μA mM^-1 cm^-2 for glucose, as well as a very low detection limit of 0.02 μM (S/N = 3) for H₂O₂ and 0.28 μM for glucose. Especially, extremely high stability can be observed, which will be beneficial for practical application.

Electrochemical Nanosensors for Sensitization of Sweat Metabolites: From Concept Mapping to Personalized Health Monitoring

Sweat contains a broad range of important biomarkers, which may be beneficial for acquiring non-invasive biochemical information on human health status. Therefore, highly selective and sensitive electrochemical nanosensors for the non-invasive detection of sweat metabolites have turned into a flourishing contender in the frontier of disease diagnosis. A large surface area, excellent electrocatalytic behavior and conductive properties make nanomaterials promising sensor materials for target-specific detection. Carbon-based nanomaterials (e.g., CNT, carbon quantum dots, and graphene), noble metals (e.g., Au and Pt), and metal oxide nanomaterials (e.g., ZnO, MnO2, and NiO) are widely used for modifying the working electrodes of electrochemical sensors, which may then be further functionalized with requisite enzymes for targeted detection. In the present review, recent developments (2018-2022) of electrochemical nanosensors by both enzymatic as well as non-enzymatic sensors for the effectual detection of sweat metabolites (e.g., glucose, ascorbic acid, lactate, urea/uric acid, ethanol and drug metabolites) have been comprehensively reviewed. Along with this, electrochemical sensing principles, including potentiometry, amperometry, CV, DPV, SWV and EIS have been briefly presented in the present review for a conceptual understanding of the sensing mechanisms. The detection thresholds (in the range of mM-nM), sensitivities, linear dynamic ranges and sensing modalities have also been properly addressed for a systematic understanding of the judicious design of more effective sensors. One step ahead, in the present review, current trends of flexible wearable electrochemical sensors in the form of eyeglasses, tattoos, gloves, patches, headbands, wrist bands, etc., have also been briefly summarized, which are beneficial for on-body in situ measurement of the targeted sweat metabolites. On-body monitoring of sweat metabolites via wireless data transmission has also been addressed. Finally, the gaps in the ongoing research endeavors, unmet challenges, outlooks and future prospects have also been discussed for the development of advanced non-invasive self-health-care-monitoring devices in the near future.

A Wearable, Textile-Based Polyacrylate Imprinted Electrochemical Sensor for Cortisol Detection in Sweat

A wearable, textile-based molecularly imprinted polymer (MIP) electrochemical sensor for cortisol detection in human sweat has been demonstrated. The wearable cortisol sensor was fabricated via layer-by-layer assembly (LbL) on a flexible cotton textile substrate coated with a conductive nanoporous carbon nanotube/cellulose nanocrystal (CNT/CNC) composite suspension, conductive polyaniline (PANI), and a selective cortisol-imprinted poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) (poly(GMA-co-EGDMA)) decorated with gold nanoparticles (AuNPs), or plated with gold. The cortisol sensor rapidly (<2 min) responded to 9.8−49.5 ng/mL of cortisol, with an average relative standard deviation (%RSD) of 6.4% across the dynamic range, indicating excellent precision. The cortisol sensor yielded an excellent limit of detection (LOD) of 8.00 ng/mL, which is within the typical physiological levels in human sweat. A single cortisol sensor patch could be reused 15 times over a 30-day period with no loss in performance, attesting to excellent reusability. The cortisol sensor patch was successfully verified for use in quantification of cortisol levels in human sweat.

High Energy Density in Combination with High Cycling Stability in Hybrid Supercapacitors

Hybrid supercapacitors are considered the next-generation energy storage equipment due to their superior performance. In hybrid supercapacitors, battery electrodes need to have large absolute capacities while displaying high cycling stability. However, enhancing areal capacity via decreasing the size of electrode materials results in reductions in cycling stability. To balance the capacity-stability trade-off, rationally designed proper electrode structures are in urgent need and still of great challenge. Here we report a high-capacity and high cycling stability electrode material by developing a nickel phosphate lamination structure with ultrathin nanosheets as building blocks. The nickel phosphate lamination electrode material exhibits a large specific capacity of 473.9 C g^-1 (131.6 mAh g^-1, 1053 F g^-1) at 2.0 A g^-1 and only about 21% capacity loss at 15 A g^-1 (375 C g^-1, 104.2 mAh g^-1, 833.3 F g^-1) in 6.0 M KOH. Furthermore, hybrid supercapacitors are constructed with nickel phosphate lamination and activated carbon (AC), possessing high energy density (42.1 Wh kg^-1 at 160 W kg^-1) as well as long cycle life (almost 100% capacity retention after 1000 cycles and 94% retention after 8000 cycles). The electrochemical performance of the nickel phosphate lamination structure not only is commensurate with the nanostructure or ultrathin materials carefully designed in supercapacitors but also has a longer cycling lifespan than them. The encouraging results show the great potential of this material for energy storage device applications.

Nickel Iron Phosphide/Phosphate as an Oxygen Bifunctional Electrocatalyst for High-Power-Density Rechargeable Zn-Air Batteries

The evolution of an effective oxygen electrocatalyst is of great importance for the widespread application of Zn-air batteries but remains an immense challenge. Thus, an efficient catalyst toward the oxygen evolution reaction and oxygen reduction reaction (OER and ORR) is highly essential for high-performance Zn-air batteries. Here, we have reported bifunctional nickel iron phosphide/phosphate (NiFeP/Pi) catalysts with various Ni/Fe ratios toward oxygen electrocatalysis in alkaline media. These catalysts are highly active toward OER and ORR, wherein NiFe(1:2)P/Pi exhibits a low OER overpotential of 0.21 V at 10 mA cm-2 and a high ORR onset potential (0.98 V vs RHE) with the lowest potential difference (ΔE = E10 - E1/2) of 0.62 V, which surpasses that of the benchmark Pt/C and RuO2 catalyst as well as those of most previously reported bifunctional catalysts. Furthermore, the NiFe(1:2)P/Pi-based Zn-air battery demonstrates a very high power density of 395 mW cm-2 and outstanding discharge capacity of 900 mAh g-1@10 mA cm-2 along with steady cyclability, maintaining 98% of the round trip efficiency over 300 cycles. These results are helpful for a good understanding of the composition-activity relation with a certain band gap toward high-performance Zn-air batteries.

Rationally designed NiMn LDH@NiCo2O4core-shell structures for high energy density supercapacitor and enzyme-free glucose sensor

Exploring high-efficiency and low-cost bifunctional electrodes for supercapacitors and sensors is significant but challenging. Most of the existing electrodes are mostly single-functional materials with simple structure. Herein, NiCo₂O₄nanowires as the core and NiMn layered double hydroxide (LDH) as the shell is directly grownin situon carbon cloth (CC) to form a heterostructure (NiMn LDH@NiCo₂O₄/CC). The performance in supercapacitors and enzyme-free glucose sensing has been systematically studied. Compared with a single NiCo₂O₄nanowire or NiMn LDH nanosheet, the heterogeneous interface produced by the unique core-shell structure has stronger electronic interaction and abundant active surface area, which shows excellent electrochemical performance. Electrochemical tests demonstrate that the NiMn LDH@NiCo₂O₄/CC core-shell electrode possesses an area specific capacitance of 2.40 F cm^-2and a rate capability of 76.22% at 20 mA cm^-2. Simultaneously, asymmetric supercapacitor is assembled with it as the positive electrode and NiFe LDH@NiCo₂O₄/CC as the negative electrode. The supercapacitor possesses an energy density of 47.74 Wh kg^-1when the power density is 175 W kg^-1, revealing excellent performance and maintains cycle stability of 93.48% after 6000 cycles at 10 mA cm^-2. Additionally, the electrode applied as enzyme-free glucose sensor electrode also displays outstanding sensitivity of 2139μA mM^-1cm^-2, wide detection range (2μM^-3mM and 4-8 mM) and low detection limit of 210 nM, representing good anti-interference performance. This work reveals the multi-metal synergy and rationally designed core-shell structure is critical to the electrochemical performance of bifunctional electrodes.

Highly sensitive non-enzymatic electrochemical glucose sensor surpassing water oxidation interference

An electrochemical non-enzymatic sensor based on a NiVP/Pi material was developed for the selective and sensitive determination of glucose. The novel sensor showed a high sensitivity of 6.04 mA μM-1 cm-2 with a lowest detection limit of 3.7 nM in a wide detection range of 100 nM-10 mM. The proposed sensor exhibited a superior selectivity without any interference from the oxygen evolution reaction during glucose sensing. We also found that this glucose sensor showed negligible interference from various interferents, such as ascorbic acid, uric acid, dopamine and sodium chloride. Additionally, a novel flexible sensor was developed by coating the NiVP/Pi over Whatman filter paper, which exhibited two linear ranges of 100 nM to 1 μM and 100 μM to 10 mM with an ultra-sensitivity of 1.130 mA μM-1 cm-2 and 0.746 mA μM-1 cm-2, respectively, in 0.1 M NaOH. The proposed sensor was tested with human blood serum samples demonstrating its practical application. Our findings provide a new route by fine tuning the composition of nickel and vanadium that sheds new light on better understanding the processes. This NiVP/Pi-based sensor offers a new approach towards the electrochemical detection of glucose, enabling glucose monitoring in a convenient way.

Pencil graphite as electrode platform for free chlorine sensors and energy storage devices

Multifunctional and low-cost electrode materials are desirable for the next-generation sensors and energy storage applications. This paper reports the use of pencil graphite as an electrode for dual applications that include the detection of free residual chlorine using electro-oxidation process and as an electrochemical energy storage cathode. The pencil graphite is transferred to cellulose paper by drawing ten times and applied for the detection of free residual chlorine, which shows a sensitivity of 27 μA mM^-1 cm^-2 with a limit of detection of 88.9 μM and linearity up to 7 mM. The sample matrix effect study for the commonly interfering ions such as NO₃^-, SO₄^2-, CO₃^2-, Cl^-, HCO₃^- shows minimal impact on free residual chlorine detection. Pencil graphite then used after cyclic voltammogram treatment as a cathode in the aqueous Zn/Al-ion battery, showing an average discharge potential plateau of ~1.1 V, with a specific cathode capacity of ~54.1 mAh g^-1 at a current of 55 mA g^-1. It maintains ~95.8% of its initial efficiency after 100 cycles. Results obtained from the density functional theory calculation is consistent with the electro-oxidation process involved in the detection of free residual chlorine, as well as intercalation and de-intercalation behavior of Al³⁺ into the graphite layers of Zn/Al-ion battery. Therefore, pencil graphite due to its excellent electro-oxidation and conducting properties, can be successfully implemented as low cost, disposable and green material for both sensor and energy-storage applications.

A longitudinally expanded Ni-based metal-organic framework with enhanced double nickel cation catalysis reaction channels for a non-enzymatic sweat glucose biosensor

Nickel-based metal-organic frameworks (Ni-MOFs) have attracted increasing attention in non-enzymatic glucose sensing. However, the insufficient active Ni cation sites from a stacked MOF layer, the unclear Ni catalysis mechanism, and the severe liquid alkaline electrolyte remain challenging for practical applications. In this work, the sonication-induced longitudinal-expansion of Ni-MOFs increases the active nickel ion sites, which not only enhances the current response to glucose detection, but also shows the oxidation peak evolution of nickel ions with different sonication times, revealing the mechanism of different glucose detection channels. The Ni-MOF sonicated for 60 min (60 min Ni-MOF) displays enhanced Ni(iii)/Ni(ii) and more significant Ni(iv)/Ni(iii) double nickel cation channels for catalyzing glucose into glucolactone compared to the 0 min Ni-MOF (without sonication), showing optimized glucose detection ability with a high sensitivity of 3297.10 μA mM-1 cm-2, a low detection limit of ∼8.97 μM (signal-to-noise = 3) and a wide linear response range from 10 to 400 μM from the cyclic voltammetry test as well as a high sensitivity of 3.03 μA mM-1 cm-2, a low detection limit of ∼1.16 μM (signal-to-noise = 3) and a wide linear response range from 10 to 2000 μM from the chronoamperometry test. More importantly, an all-solid-state glucose biosensor using a PVA/NaOH solid-state electrolyte and a disposable 60 min Ni-MOF working electrode is assembled for non-enzymatic sweat glucose detection.

Permeable Weldable Elastic Fiber Conductors for Wearable Electronics

Elastic fiber conductors are advantageous for applications in wearable electronics due to their small size, light weight, and excellent integration ability. Here, we report the fabrication of elastic fiber conductors with a three-dimensional (3D) porous structure using electrospun thermoplastic elastomer (TPE) microfibers and silver nanoparticles (AgNPs) as the building blocks. With the 3D porous structure, such a fiber is highly permeable to gases and liquids. As such, the performance of the fiber in many applications of wearable electronics (especially wearable sensors and detectors) can be improved significantly. Benefitting from the excellent processability of TPE and dispersibility of AgNPs, the fiber is highly compatible with thermal and solvent welding. In addition, the fiber also possesses super stretchability, high conductivity, and robust endurance to deformation. As a proof-of-concept application, we demonstrate that a rope-shaped capacitor made by plying one pair of such fibers can detect the volume change of artificial sweat with 17-times higher sensitivity than the capacitor using nonporous fibers as electrodes. We further demonstrate that, by integrating two groups of perpendicularly arranged fibers into a monolithic porous mat, sensitive matrix-addressed monitoring of artificial sweat can be realized.

Regulating the electrochemical behaviours of a hierarchically structured Co3(PO4)2/Ni-Co-O for a high-performance all-solid-state supercapacitor

Battery-type materials (e.g., transition metal phosphates) have been intensely explored in supercapacitors due to their rich electroactive sites and high theoretical capacity. Yet poor rate performance, resulting in a low energy density at high current density, limits their further applications. Herein, an improvement in rate performance resulting from enhanced surface capacitive behaviour contribution has been observed in a hierarchically structured Co3(PO4)2/Ni-Co-O@Ni foam (CPNO-12). The optimized CPNO-12 synthesized through a facile hydrothermal treatment also exhibits a striking gravimetric and areal capacity of 1410C g-1 (14 100 mC cm-2) at 5 mA cm-2 and superb cyclability (91% of retention at 50 mA cm-2 after 12 000 cycles), which can be attributed to its unique hierarchical porous structure and high mass loading per area. More importantly, a high-performance all-solid-state asymmetric supercapacitor with CPNO-12 and Fe2P/graphene hydrogel@Ni foam as positive and negative electrodes respectively has been assembled; the device delivering a maximum energy density of 95 W h kg-1 (32 mW h cm-3) and maximum power density of 4000 W kg-1 (800 mW cm-3) has the potential to power sophisticated systems. These attractive performances confirm that an enhancement of capacitive behaviour in battery-type materials holds the promise for fabricating high-performance supercapacitors.

Flexible molecularly imprinted electrochemical sensor for cortisol monitoring in sweat

A selective cortisol sensor based on molecularly imprinted poly(glycidylmethacrylate-co ethylene glycol dimethacrylate) (poly(GMA-co-EGDMA)) has been demonstrated for detection of cortisol in human sweat. The non-enzymatic biomimetric flexible sweat sensor was fabricated inexpensively by layer by layer (LbL) assembly. The sensor layers comprised a stretchable polydimethylsiloxane (PDMS) base with carbon nanotubes-cellulose nanocrystals (CNC/CNT) conductive nanoporous nanofilms. The imprinted (MIP) poly(GMA-co-EGDMA) deposited on the CNC/CNT was the cortisol biomimetric receptor. Rapid in analyte response (3 min), the cortisol MIP sensor demonstrated excellent performance. The sensor has a limit of detection (LOD) of 2.0 ng/mL ± 0.4 ng/mL, dynamic range of 10-66 ng/mL, and a sensor reproducibility of 2.6% relative standard deviation (RSD). The MIP sensor also had high cortisol specificity and was inherently blind to selected interfering species including glucose, epinephrine, β-estradiol, and methoxyprogestrone. The MIP was four orders of magnitude more sensitive than its non-imprinted (NIP) counterpart. The MIP sensor remains stable over time, responding proportionately to doses of cortisol in human sweat. Graphical abstract.

Phosphate microbial mineralization removes nickel ions from electroplating wastewater

Nickel ions in electroplating wastewater can be removed by the bio-mineralization method. Bacillus subtilis can produce alkaline phosphatase, which hydrolyzes organophosphate monoesters and produces phosphate ions. Fourier-transform infrared spectroscopy (FTIR) showed that the precipitated material contains phosphate ions. X-ray diffraction (XRD) showed that nickel ions in electroplating wastewater react with Bacillus subtilis and organophosphate monoesters to obtain nickel phosphate octahydrate (Ni₃(PO₄)₂·8H₂O). The removal efficiency of nickel ions could reach 76.41% with the optimum content of the organophosphate monoester (0.02 mol), Bacillus subtilis powder (2 g), pH (6), standing time (36 h), and reaction temperature (25 °C) in the medium solution (100 mL). The average particle size of Ni₃(PO₄)₂·8H₂O was 80.51 nm, which was calculated by the Scherrer formula. The Lorentz-Transmission Electron Microscope (L-TEM) further showed that Ni₃(PO₄)₂·8H₂O was composed of clusters of irregular nanoparticles, and the individual particle size was in the range of 40-90 nm. The TGA curve shows that the mass loss of crystal water was 25.45%, which was close to the theoretical total mass loss of 28.24% in bio-Ni₃(PO₄)₂·8H₂O.

A high-performance asymmetric supercapacitor designed with a three-dimensional interconnected porous carbon framework and sphere-like nickel nitride nanosheets

The novel asymmetric supercapacitor was assembled based on a three-dimensional (3D) interconnected porous carbon framework as the negative electrode and 3D sphere-like nickel nitride nanosheets as the positive electrode in aqueous electrolyte.

A review of the advanced developments of electrochemical sensors for the detection of toxic and bioactive molecules

The recent developments made regarding the novel, cost-effective, and environmentally friendly nanocatalysts for the electrochemical sensing of biomolecules, pesticides, nitro compounds and heavy metal ions are discussed in this review article.

Cobalt Phosphate Nanostructures for Non-Enzymatic Glucose Sensing at Physiological pH

Nanostructured materials have potential as platforms for analytical assays and catalytic reactions. Herein, we report the synthesis of electrocatalytically active cobalt phosphate nanostructures (CPNs) using a simple, low-cost, and scalable preparation method. The electrocatalytic properties of CPNs toward the electrooxidation of glucose (Glu) were studied by cyclic voltammetry and chronoamperometry in relevant biological electrolytes, such as phosphate-buffered saline (PBS), at physiological pH (7.4). Using CPNs, Glu detection could be achieved over a wide range of biologically relevant concentrations, from 1 to 30 mM Glu in PBS, with a sensitivity of 7.90 nA/mM cm² and a limit of detection of 0.3 mM, thus fulfilling the necessary requirements for human blood Glu detection. In addition, CPNs showed a high structural and functional stability over time at physiological pH. The CPN-coated electrodes could also be used for Glu detection in the presence of interfering agents (e.g., ascorbic acid and dopamine) and in human serum. Density functional theory calculations were performed to evaluate the interaction of Glu with different faceted cobalt phosphate surfaces; the results revealed that specific surface presentations of under-coordinated cobalt led to the strongest interaction with Glu, suggesting that enhanced detection of Glu by CPNs can be achieved by lowering the surface coordination of cobalt. Our results highlight the potential use of phosphate-based nanostructures as catalysts for electrochemical sensing of biochemical analytes.

Sensor systems for bacterial reactors: A new flavin-phenol composite film for the in situ voltammetric measurement of pH

Monitoring pH within microbial reactors has become an important requirement across a host of applications ranging from the production of functional foods (probiotics) to biofuel cell systems. An inexpensive and scalable composite sensor capable of monitoring the pH within the demanding environments posed by microbial reactors has been developed. A custom designed flavin derivative bearing an electropolymerisable phenol monomer was used to create a redox film sensitive to pH but free from the interferences that can impede conventional pH systems. The film was integrated within a composite carbon-fibre-polymer laminate and was shown to exhibit Nernstian behaviour (55 mV/pH) with minimal drift and robust enough to operate within batch reactors.