A Novel Enzymatic Glucose Biosensor and Nonenzymatic Hydrogen Peroxide Sensor Based on (3‐Aminopropyl) Triethoxysilane Functionalized Reduced Graphene Oxide

In the present study, a novel enzymatic glucose biosensor using glucose oxidase (GOx) immobilized into (3‐aminopropyl) triethoxysilane (APTES) functionalized reduced graphene oxide (rGO‐APTES) and hydrogen peroxide sensor based on rGO‐APTES modified glassy carbon (GC) electrode were fabricated. Nafion (Nf) was used as a protective membrane. For the characterization of the composites, Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffractometer (XRD), and transmission electron microscopy (TEM) were used. The electrochemical properties of the modified electrodes were investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The resulting Nf/rGO‐APTES/GOx/GC and Nf/rGO‐APTES/GC composites showed good electrocatalytical activity toward glucose and H₂O₂, respectively. The Nf/rGO‐APTES/GC electrode exhibited a linear range of H₂O₂ concentration from 0.05 to 15.25 mM with a detection limit (LOD) of 0.017 mM and sensitivity of 124.87 μA mM⁻¹ cm⁻². The Nf/rGO‐APTES/GOx/GC electrode showed a linear range of glucose from 0.02 to 4.340 mM with a LOD of 9 μM and sensitivity of 75.26 μA mM⁻¹ cm⁻². Also, the sensor and biosensor had notable selectivity, repeatability, reproducibility, and storage stability.     

Minimization of Interferences in Flow Injection Amperometric Glucose Biosensor Based on Oxidation of Enzymatically‐produced H2O2

One of the major problems in amperometric biosensors based on detection of H₂O₂ produced by enzymatic reaction between oxidase enzymes and substrate is the interference of redox active compounds such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). To minimize these interferences, sodium bismuthate was used for the first time as an insoluble pre‐oxidant in the flow injection (FI) amperometric glucose biosensor at a Glucose oxidase (GOx) immobilized Pt/Pd bimetallic modified pre‐anodized pencil graphite electrode (p.PGE). In this context, these interfering compounds were injected into a flow injection analysis (FIA) system using an injector which was filled with NaBiO₃. Thus, these interferents were converted into their redox inactive oxidized forms before reaching the electrode in the flow cell. While glucose was not influenced by the pre‐oxidant in the injector, the huge oxidation peak currents of the interferents decreased significantly in the biosensor. FI amperometric current time curves showed that the AA, DA and UA were minimized by 96 %, 86 %, and 98 % respectively, in the presence of an equivalent concentration of interferences in a 1.0 mM glucose solution. The proposed FI amperometric glucose biosensor exhibits a wide linear range (0.01–10 mM, R²=0.9994) with a detection limit of 2.4×10^?3 mM. Glucose levels in the artificial serum and two real samples were successfully determined using the fabricated FI amperometric biosensor.     

Specific “Unlocking” of a Nanozyme‐Based Butterfly Effect To Break the Evolutionary Fitness of Chaotic Tumors

Chaos and the natural evolution of tumor systems can lead to the failure of tumor therapies. Herein, we demonstrate that iridium oxide nanoparticles (IrO_x) possess acid‐activated oxidase and peroxidase‐like functions and wide pH‐dependent catalase‐like properties. The integration of glucose oxidase (GOD) unlocked the oxidase and peroxidase activities of IrO_x by the production of gluconic acid from glucose by GOD catalysis in cancer cells, and the produced H₂O₂ was converted into O₂ to compensate its consumption in GOD catalysis owing to the catalase‐like function of the nanozyme, thus resulting in the continual consumption of glucose and the self‐supply of substrates to generate superoxide anion and hydroxyl radical. Moreover, IrO_x can constantly consume glutathione (GSH) by self‐cyclic valence alternation of Ir^IV and Ir^III. These cascade reactions lead to a “butterfly effect” of initial starvation therapy and the subsequent pressure of multiple reactive oxygen species (ROS) to completely break the self‐adaption of cancer cells.     

An Enzyme‐free H2O2 Sensor Based on Poly(2‐Aminophenylbenzimidazole)/Gold Nanoparticles Coated Pencil Graphite Electrode

A poly(2‐aminophenylbenzimidazole)/gold nanoparticles (P2AB/AuNPs) coated disposable pencil graphite electrode (PGE) was fabricated as an enzyme‐free sensor for the H₂O₂ determination. P2AB/AuNPs and P2AB were successfully synthesized electrochemically on PGE in acetonitrile for the first time. The coatings were characterized by scanning electron microscopy, X‐ray diffraction spectroscopy, Energy‐dispersive X‐ray spectroscopy, Surface‐enhanced Raman spectroscopy, and UV‐Vis spectroscopy. AuNPs interacted with P2AB as carrier enhances the electrocatalytic activity towards reduction of H₂O₂. The analytical performance was evaluated in a 100 mM phosphate buffer solution at pH 6.5 by amperometry. The steady state current vs. H₂O₂ concentration is linear in the range of 0.06 to 100 mM (R²=0.992) with a limit of detection 3.67×10^?5 M at ?0.8 V vs. SCE and no interference is caused by ascorbic acid, dopamine, uric acid, and glucose. The examination for the sensitive determination of H₂O₂ was conducted in commercially available hair oxidant solution. The results demonstrate that P2AB/AuNPs/PGE has potential applications as a sensing material for quantitative determination of H₂O₂.     

A Membraneless Glucose/O2 Biofuel Cell Based on Pd Aerogels

In this study, we introduce the first membraneless glucose/O₂ biofuel cell using Pd‐based aerogels as electrode materials. The bioanode was fabricated with a coimmobilized mediator and glucose oxidase for the oxidation of glucose, in which ferrocenecarboxylic acid was integrated into a three‐dimensional porous beta‐cyclodextrin‐modified Pd aerogel to mediate the bioelectrocatalytic reaction. Bilirubin oxidase and Pd–Pt alloy aerogel were confined to an electrode surface, which realized the direct bioelectrocatalytic function for the reduction of O₂ to H₂O with a synergetic effect at the biocathode. By employing these two bioelectrodes, the assembled glucose/O₂ biofuel cell showed a maximum power output of 20 μW cm^?2 at 0.25 V.     

Novel Sn Doped Co3O4 Thin Film for Nonenzymatic Glucose Bio‐Sensor and Fuel Cell

A facile chemical solution deposition via two‐step spin coating technique was used to fabricate nano‐particulate novel Sn doped Co₃O₄ thin film for glucose sensor and fuel cell applications. Substitution of Sn into Co₃O₄ host lattice lead to a remarkable increase in the electrocatalytic activity of the Co₃O₄ electrode material. Film thickness played a significant role in enhancing the charge transferability of the electrode as was observed from electrochemical impedance spectroscopy (EIS). The best sensor exhibited two wide linear response ranges (2 μM up to ∼0.5 mM and 0.6 mM up to ∼5.5 mM respectively) with sensitivities of 921 and 265 μA cm⁻² mM⁻¹ respectively and low limit of detection of 100 nM (S/N=3). The sensor was very selective towards glucose in the presence of various interference and showed long term stability. Moreover, the developed thin film modified electrode could generate one electron current in nonenzymatic fuel cell setup at room temperature.     

Amperometric Glucose Biosensor Based on Pt‐Pd Nanoparticles Supported by Reduced Graphene Oxide and Integrated with Glucose Oxidase

A novel glucose biosensor was developed based on the immobilization of glucose oxidase (GOx) on reduced graphene oxide incorporated with electrochemically deposited platinum and palladium nanoparticles (PtPdNPs). Reduced graphene oxide (RGO) was more hybridized by chemical and heat treatment. Bimetallic nanoparticles were deposited electrochemically on the RGO surface for potential application of the Pd? Pt alloy in biosensor preparation. The as‐prepared hybrid electrode exhibited high electrocatalytic activities toward H₂O₂, with a wide linear response range from 0.5 to 8 mM (R²=0.997) and high sensitivity of 814×10^?6 A/mMcm². Furthermore, glucose oxidase with active material was integrated by a simple casting method on the RGO/PdPtNPs surface. The as‐prepared biosensor showed good amperometric response to glucose in the linear range from 2 mM to 12 mM, with a sensitivity of 24×10^?6 A/mMcm², a low detection limit of 0.001 mM, and a short response time (5 s). Moreover, the effect of interference materials, reproducibility and the stability of the sensor were also investigated.     

Immobilized Fullerene C60‐Enzyme‐Based Electrochemical Glucose Sensor

A mixed‐valence cluster of cobalt(II) hexacyanoferrate and fullerene C60‐enzyme‐based electrochemical glucose sensor was developed. A water insoluble fullerene C60‐glucose oxidase (C60‐GOD) was prepared and applied as an immobilized enzyme on a glassy carbon electrode with cobalt(II) hexacyanoferrate for analysis of glucose. The glucose in 0.1 M KCl/phosphate buffer solution at pH = 6 was measured with an applied electrode potential at 0.0 mV (vs Ag/AgCl reference electrode). The C60‐GOD‐based electrochemical glucose sensor exhibited efficient electro‐catalytic activity toward the liberated hydrogen peroxide and allowed cathodic detection of glucose. The C60‐GOD electrochemical glucose sensor also showed quite good selectivity to glucose with no interference from easily oxidizable biospecies, e.g. uric acid, ascorbic acid, cysteine, tyrosine, acetaminophen and galactose. The current of H₂O₂ reduced by cobalt(II) hexacyanoferrate was found to be proportional to the concentration of glucose in aqueous solutions. The immobilized C60‐GOD enzyme‐based glucose sensor exhibited a good linear response up to 8 mM glucose with a sensitivity of 5.60 × 10² nA/mM and a quite short response time of 5 sec. The C60‐GOD‐based glucose sensor also showed a good sensitivity with a detection limit of 1.6 × 10^‐6 M and a high reproducibility with a relative standard deviation (RSD) of 4.26%. Effects of pH and temperature on the responses of the immobilized C60‐GOD/cobalt(II) hexacyanoferrate‐based electrochemical glucose sensor were also studied and discussed.     

A Single Drop Fabrication of the Cholesterol Biosensor Based on Synthesized NiFe2O4NPs Dispersed on PDDA‐CNTs

A cholesterol biosensor based on cholesterol oxidase‐poly(diallyldimethylammonium chloride)‐carbon nanotubes‐nickel ferrite nanoparticles (ChOx‐PDDA‐CNTs‐NiFe₂O₄NPs) solution is easily fabricated by using a single dropping step on a glassy carbon electrode (GCE) surface. This technique is an alternative way to reduce complexity, cost and time to produce the biosensor. The uniformly dispersed materials on the electrode surface enhance the catalytic reaction of cholesterol oxidase and electron transfer from the oxidation of hydrogen peroxide in the system. The nickel ferrite nanoparticles were synthesized by co‐precipitation and calcination at various temperatures. These nanoparticles were then characterized using field emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and X‐ray diffraction (XRD). The synthesized material calcined at 700 °C was well defined and presented the octahedral metal stretching with cubic NiFe₂O₄NPs phase. In cyclic voltammetric study, the ChOx‐PDDA‐CNTs‐NiFe₂O₄NPs/GCE showed 0.43 s⁻¹ charge transfer rate constant (K _s), 7.79×10⁻⁶ cm² s⁻¹ diffusion coefficient value (D ), 0.13 mm² electroactive surface area (A _e) and 3.58×10⁻⁸ mol cm⁻² surface concentration ( ). This modified electrode exhibits stability in term of percent relative standard deviation (%RSD=0.62 %, n=10), reproducibility (%RSD=0.81, n=10), high sensitivity (25.76 nA per mg L⁻¹ cm⁻²), linearity from 1 to 5,000 mg L⁻¹ (R²=0.998) with a low detection limit (0.50 mg L⁻¹). Its Michaelis‐Menten constant (K _m) was 0.14 mM with 0.92 μA maximum current (I _max) and demonstrated good selectivity without the effects of electroactive species such as ascorbic acid, glucose and uric acid. The cholesterol biosensor was successfully applied to determine cholesterol levels in human blood samples, showing promise due to its simplicity and availability.     

Electrochemically Prepared Three‐dimensional Porous Nitrogen‐doped Graphene Modified Electrode for Non‐enzymatic Detection of Hydrogen Peroxide

A facile and green electrochemical method for the fabrication of three‐dimensional porous nitrogen‐doped graphene (3DNG) modified electrode was reported. This method embraces two consecutive steps: First, 3D graphene/polypyrrole (ERGO/PPy) composite was prepared by electrochemical co‐deposition of graphene and polypyrrole on a gold foil. Subsequently, the ERGO/PPy composite modified gold electrode was annealed at high temperature. Thus 3DNG modified electrode was obtained. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to characterize the structure and morphology of the electrode. The electrode exhibits excellent electroanalytical performance for the reduction of hydrogen peroxide (H₂O₂). By linear sweep voltammetric measurement, the cathodic peak current was linearly proportional to H₂O₂ concentration in the range from 0.6 μM to 2.1 mM with a sensitivity of 1.0 μA μM⁻¹ cm⁻². The detection limit was ascertained to be 0.3 μM. The anti‐interference ability, reproducibility and stability of the electrode were carried out and the electrode was applied to the detection of H₂O₂ in serum sample with recoveries from 98.4 % to 103.2 %.     

Fabrication of a Highly Sensitive Glucose Biosensor Based on Immobilization of Osmium Complex and Glucose Oxidase onto Carbon Nanotubes Modified Electrode

In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxygen and H₂O₂ in physiological pH solutions. Electroless deposition at a short period of time (60 s), was used for strong and irreversible adsorption of 1,4,8,12‐tetraazacyclotetradecane osmium(III) chloride (Os(III)LCl₂) ClO₄ onto single‐walled carbon nanotubes (SWCNTs) modified GC electrode. The modified electrode shows a pair of well defined and reversible redox couple, Os(IV)/Os(III) at wide pH range (1–8). The glucose biosensor was fabricated by covering a thin film of glucose oxidase onto CNTs/Os‐complex modified electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The fabricated biosensor shows high sensitivity, 826.3 nA μM^?1cm^?2, low detection limit, 56 nM, fast response time <3 s and wide calibration range 1.0 μM–1.0 mM. The biosensor has been successfully applied to determination of glucose in human plasma. Because of relative low applied potential, the interference from electroactive existing species was minimized, which improved the selectivity of the biosensor. The apparent Michaelis‐Menten constant of GOx on the nanocomposite, 0.91 mM, exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this glucose biosensor.     

A Comparison of a Nanostructured Enzymeless Au/Fe2O3/MWCNTs/GCE Electrode and a GOx Modified One in Electrocatalytic Detection of Glucose

Acid functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were decorated with Au and Fe₂O₃ nanoparticles (FeONPs) and deposited on glassy carbon electrode (GCE). The resulting hybrid Au/Fe₂O₃/f‐MWCNTs/GCE electrode and the one further modified by glucose oxidase were compared for detection of glucose. FeONPs and Au were deposited on the f‐MWCNTs by sonication‐assisted precipitation and deposition‐precipitation methods, respectively. The morphology and structure of the samples were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. A uniform distribution of FeONPs with an average size of 5 nm increased the surface area of functionalized nanotubes from 39 to 50 m²/g. The electrocatalytic glucose detection on the modified electrodes was evaluated using cyclic voltammetry and chronoamperometry in 0.1 M phosphate buffer solution at pH 7.0. The non‐enzymatic and enzymatic electrodes show sensitivity of 512.4 and 921.4 mA/mM.cm² and detection limit of 1.7 and 0.9 mM, respectively. The enzymatic and enzymeless electrodes retained more than 70 % and 80 % of their cathodic faradic current after 70 days, respectively. The sensing mechanism of the non‐enzymatic biosensor is described through the reaction of glucose with iron (III) ions, while in the case of enzymatic electrode, glucose is oxidized by glucose oxidase.     

Preparation of non‐covalent Metalloporphyrin/C60 Composite and its Electrocatalysis to Hydrogen Peroxide

Three non‐covalent metallotetraphenylporphyrin/fullerene (MTPPS₄ (M=Zn²⁺, Fe²⁺, Co²⁺)/C₆₀) nanocomposites were prepared by π‐π molecular interaction and characterized by scanning electron microscopy and UV‐Vis absorption spectroscopy. Electrocatalytic studies indicated that the MTPPS₄/C₆₀ nanocomposites which were embedded in TOAB film on the glassy carbon electrode (GCE) (TOAB/MTPPS₄/C₆₀/GCE) exhibited a high electrocatalytic activity for H₂O₂. MTPPS₄ enhanced the electrocatalytic ability of C₆₀ in the increasing order of TOAB/ZnTPPS₄/C₆₀/GCE, TOAB/FeTPPS₄/C₆₀/GCE and TOAB/CoTPPS₄/C₆₀/GCE. The measurement with the differential pulse voltammetry (DPV) exhibited that there is a well‐defined linear relationship between the reduction currents and H₂O₂ concentrations in the range from 0.3 to 1.0 mM, with the detection limit of 0.07 mM at the TOAB/ZnTPPS₄/C₆₀/GCE electrode, of 0.08 mM at the TOAB/FeTPPS₄/C₆₀/GCE electrode, of 0.04 mM at the TOAB/CoTPPS₄/C₆₀/GCE electrode, respectively. The biosensors showed a good anti‐interfering ability towards glucose, ascorbic acid and L‐cysteine and a high potential practicality.     

Highly Oriented Nitrogen-doped Carbon Nanotube Integrated Bimetallic Cobalt Copper Organic Framework for Non-enzymatic Electrochemical Glucose and Hydrogen Peroxide Sensor

The hierarchical three-dimensional nitrogen-doped carbon nanotube anchored bimetallic cobalt copper organic framework (NCNT MOF CoCu) is successfully synthesized by the direct growth approach using the high-temperature carbonization of bimetallic cobalt copper organic framework (MOF CoCu-500). The as-prepared NCNT MOF CoCu nanostructure possesses high-level activity for both glucose and hydrogen peroxide (H₂O₂) sensing molecules. The cyclic voltammetry (CV) and chronoamperometry (CA) studies demonstrate excellent electrocatalytic performance for the oxidation of glucose with a linear range of 0.05 to 2.5 mM, high sensitivity of 1027 μA mM⁻¹cm⁻², and the lowest detection limit of 0.15 μM. Similarly, the NCNT MOF CoCu nanostructure showed significantly higher H₂O₂ activity with a linear range of 0.05 to 3.5 mM, high sensitivity of 639.5 μA mM⁻¹cm⁻², and the lowest detection limit of 0.206 μM. Thanks to its special hierarchical nanoarchitecture, homogeneous nitrogen-doped carbon nanotubes, and highly graphitized carbon, which may be increased the synergistic effect between bimetallic CoCu and NCNT in the organic framework. The potentially effective fabricated sensor was also used as a suitable probe for the detection of glucose and H₂O₂ in the analysis of the real samples.     

Electrochemical properties of violuric acid and oxidase biosensor preparation

The electrochemical properties of violuric acid (VA) have been investigated at pH 4.0–10.0 by using cyclic voltammetry on a glassy carbon electrode. The peak current was proportional to the square root of the potential scan rate. The calculated diffusion coefficient was 2.0±0.7×10⁻⁶ cm² s⁻¹. The formal oxidation–reduction potential of VA was 0.63 V versus SCE at pH 7.0. The kinetics of VA interaction with reduced glucose oxidase (GO) was explored in the electrocatalytical system. A typical electrocatalytical wave was generated in the presence of the VA and glucose. An apparent k_ox calculated by using the Nicholson–Shain function was 1.85×10⁶ M⁻¹ s⁻¹ at pH 7.0 and 25 °C. Glucose and l-lactate bioelectrodes were prepared by adsorbing the GO and l-lactate oxidase (LO) onto the VA-modified graphite electrode. The electrode was poised at 0.6 V versus SCE and linear response was obtained over the range of 4–20 mM glucose and 2–12 mM l-lactate, respectively.     

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed “diaphragms” that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H₂O₂ relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3 mg GOD per 1 mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H₂O₂, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6 s), broad detection range (10 μM to 10 mM), high sensitivity (143.5 μA mM⁻¹ cm⁻²) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1 μM to 0.83 mM, sensitivity of 494.9 μA mM⁻¹ cm⁻², and detection limit of 0.02 μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors.     

A Photoelectrochemical Biosensor Fabricated using Hierarchically Structured Gold Nanoparticle and MoS2 on Tannic Acid Templated Mesoporous TiO2

In a tannic acid assisted synthesis of mesoporous TiO₂, tannic acid was used as a cost effective and non‐toxic template for pore formation. Meanwhile, a gold nanoparticles (Au NPs) deposited TiO₂ nanocomposite was coated on an indium tin oxide electrode for the fabrication of a photoelectrochemical (PEC) biosensing system. Upon the formation of anatase structure, the electrode was coated with MoS₂ for effective visible light absorption. The mesoporous structure led to an enhanced surface area by improving Au NPs and glucose oxidase adsorption. Incorporation of Au NPs led to an enhanced photonic efficiency due to the generation of Schottky barriers. The obtained nanocomposite was used for the light‐driven, real‐time, and selective PEC glucose sensing. Under visible light irradiation, the enzyme immobilized electrodes yielded significant photocurrent improvement owing to the releasing electron donor H₂O₂. The obtained PEC biosensor demonstrated acceptable reproducibility and stability with a sensitivity of 4.42 μA mM^?1 cm^?2 and a low detection limit of 1.2 μM glucose. Also, the linear measurement range was found to be 0.004–1.75 mM glucose. The results indicated that the proposed production method of mesoporous TiO₂ will pave the way for a green chemistry based porous material production, along with the extension of the implementation of semiconductors in PEC biosensing systems.     

Six two‐ and three‐component ammonium carboxylate salt structures with a ladder‐type hydrogen‐bonding motif,three incorporating neutral carboxylic acid molecules

Six ammonium carboxylate salts are synthesized and reported, namely 2‐propylammonium benzoate, C₃H₁₀N⁺·C₇H₅O₂⁻, (I), benzylammonium (R)‐2‐phenylpropionate, C₆H₁₀N⁺·C₉H₉O₂⁻, (II), (RS)‐1‐phenylethylammonium naphthalene‐1‐carboxylate, C₈H₁₂N⁺·C₁₁H₇O₂⁻, (III), benzylammonium–benzoate–benzoic acid (1/1/1), C₆H₁₀N⁺·C₇H₅O₂⁻·C₇H₆O₂, (IV), cyclopropylammonium–benzoate–benzoic acid (1/1/1), C₃H₈N⁺·C₇H₅O₂⁻·C₇H₆O₂, (V), and cyclopropylammonium–ea‐cis‐cyclohexane‐1,4‐dicarboxylate–ee‐trans‐cyclohexane‐1,4‐dicarboxylic acid (2/1/1), 2C₃H₈N⁺·C₈H₁₀O₄²⁻·C₈H₁₂O₄, (VI). Salts (I)–(III) all have a 1:1 ratio of cation to anion and feature three N⁺—H...O⁻ hydrogen bonds which form one‐dimensional hydrogen‐bonded ladders. Salts (I) and (II) have type II ladders, consisting of repeating R₄³(10) rings, while (III) has type III ladders, in this case consisting of alternating R₄²(8) and R₄⁴(12) rings. Salts (IV) and (V) have a 1:1:1 ratio of cation to anion to benzoic acid. They have type III ladders formed by three N⁺—H...O⁻ hydrogen bonds, while the benzoic acid molecules are pendant to the ladders and hydrogen bond to them via O—H...O⁻ hydrogen bonds. Salt (VI) has a 2:1:1 ratio of cation to anion to acid and does not feature any hydrogen‐bonded ladders; instead, the ionized and un‐ionized components form a three‐dimensional network of hydrogen‐bonded rings. The two‐component 1:1 salts are formed from a 1:1 ratio of amine to acid. To create the three‐component salts (IV)–(VI), the ratio of amine to acid was reduced so as to deprotonate only half of the acid molecules, and then to observe how the un‐ionized acid molecules are incorporated into the ladder motif. For (IV) and (V), the ratio of amine to acid was reduced to 1:2, while for (VI) the ratio of amine to acid required to deprotonate only half the diacid molecules was 1:1.     

A novel conductance glucose biosensor in ultra-low ionic strength solution triggered by the oxidation of Ag nanoparticles

A simple, sensitive and effective method to detect glucose in ultra-low ionic strength solution containing citrate-capped silver nanoparticles (CCAgNPs) was developed by monitoring the change of solution conductance. Glucose was catalyzed into gluconic acid firstly by glucose oxidase in an O₂-saturated solution accompanied by the reduction of O₂ into hydrogen peroxide (H₂O₂). Then, CCAgNPs was oxidized by H₂O₂ into Ag⁺ and the capping regent of citrate was released at the same time. All these resulted Ag⁺, gluconic acid and the released citrate would contribute to the increase of solution ionic strength together, leading to a detectable increase of solution conductance. And a novel conductance glucose biosensor was developed with a routine linear range of 0.06–4.0 mM and a suitable detection limit of 18.0 μM. The novel glucose biosensor was further applied in energy drink sample and proven to be suitable for practical system with low ionic strength. The proposed conductance biosensor achieved a significant breakthrough of glucose detection in ultra-low ionic strength media.     

An Amperometric Glucose Biosensor Based on Poly (Pyrrole‐2‐Carboxylic Acid)/Glucose Oxidase Biocomposite

A newly developed amperometric glucose biosensor based on graphite rod (GR) working electrode modified with biocomposite consisting of poly (pyrrole‐2‐carboxylic acid) (PCPy) particles and enzyme glucose oxidase (GOx) was investigated. The PCPy particles were synthesized by chemical oxidative polymerization technique using H₂O₂ as initiator of polymerization reaction and modified covalently with the GOx (PCPy‐GOx) after activation of carboxyl groups located on the particles surface with a mixture of N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS). Then the PCPy‐GOx biocomposite was dispersed in a buffer solution containing a certain amount of bovine serum albumin (BSA). The resulting biocomposite suspension was adsorbed the on GR electrode surface with subsequent solvent airing and chemical cross‐linking of the proteins with glutaraldehyde vapour (GR/PCPy‐GOx). It was determined that the current response of the GR/PCPy‐GOx electrodes to glucose measured at +300 mV vs Cl reference electrode was influenced by the duration of the PCPy particles synthesis, pH of the GOx solution used for the PCPy particles modification and the amount of immobilized PCPy‐GOx biocomposite. An optimal pH of buffer solution for operation of the biosensor was found to be 8.0. Detection limit was determined as 0.039 mmol L⁻¹ according signal to noise ratio (S/N: 3). The proposed glucose biosensor was tested in human serum samples.