A cyclodextrin host-guest recognition approach to an electrochemical sensor for simultaneous quantification of serotonin and dopamine

An electrochemical sensor for simultaneous quantification of serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) using a β-cyclodextrin/poly(N-acetylaniline)/carbon nanotube composite modified carbon paste electrode has been developed. Synergistic effect of multi-walled carbon nanotube (MWCNT) in addition to the pre-concentrating effect of β-cyclodextrin (β-CD) as well as its different inclusion complex stability with 5-HT and DA was used to construct an electrochemical sensor for quantification of these important neurotransmitters. The overlapping anodic peaks of 5-HT and DA at 428 mV on bare electrode resolved in two well-defined voltammetric peaks at 202 and 363 mV vs. Ag/AgCl respectively. The oxidation mechanism of 5-HT and DA on the surface of the electrode was investigated by cyclic voltammetry and it was found that the electrode processes are pH dependent and electrochemical oxidation of 5-HT is totally irreversible while the electrode gave a more reversible process to DA. Under optimized conditions, linear calibration curves were obtained in the range of about 4-200 μM with a detection limits down to sub-μM levels (S/N=3) after 20-s accumulation, for both. The proposed sensor was shown to be remarkably selective for 5-HT and DA in matrices containing different species including ascorbic acid and uric acid. The suitability of the developed method was tested for the determination of 5-HT and DA in the Randox Synthetic Plasma samples and acceptable recoveries were obtained for a set of spiked samples.     

Simultaneous determination of catecholamines, uric acid and ascorbic acid at physiological levels using poly(N-methylpyrrole)/Pd-nanoclusters sensor

An interesting electrochemical sensor has been constructed by the electrodeposition of palladium nanoclusters (Pd_nano) on poly(N-methylpyrrole) (PMPy) film-coated platinum (Pt) electrode. Cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy were used to characterize the properties of the modified electrode. It was demonstrated that the electroactivity of the modified electrode depends strongly on the electrosynthesis conditions of the PMPy film and Pd_nano. Moreover, the modified electrode exhibits strong electrocatalytic activity toward the oxidation of a mixture of dopamine (DA), ascorbic acid (AA), and uric acid (UA) with obvious reduction of overpotentials. The simultaneous analysis of this mixture at conventional (Pt, gold [Au], and glassy carbon) electrodes usually struggles. However, three well-resolved oxidation peaks for AA, DA, and UA with large peak separations allow this modified electrode to individually or simultaneously analyze AA, DA, and UA by using differential pulse voltammetry (DPV) with good stability, sensitivity, and selectivity. This sensor is also ideal for the simultaneous analysis of AA, UA and either of epinephrine (E), norepinephrine (NE) or l-DOPA. Additionally, the sensor shows strong electrocatalytic activity towards acetaminophen (ACOP) and other organic compounds. The calibration curves for AA, DA, and UA were obtained in the ranges of 0.05 to 1 mM, 0.1 to 10 μM, and 0.5 to 20 μM, respectively. The detection limits (signal/noise [S/N] = 3) were 7 μM, 12 nM, and 27 nM for AA, DA, and UA, respectively. The practical application of the modified electrode was demonstrated by measuring the concentrations of AA, DA, and UA in injection sample, human serum, and human urine samples, respectively, with satisfactory results. The reliability and stability of the modified electrode gave a good possibility for applying the technique to routine analysis of AA, DA, and UA in clinical tests.     

Simultaneous and sensitive determination of a quaternary mixture of AA, DA, UA and Trp using a modified GCE by iron ion-doped natrolite zeolite-multiwall carbon nanotube

The evaluation of a novel modified glassy carbon electrode modified with iron ion-doped natrolite zeolite-multiwalled carbon nanotube for the simultaneous and sensitive determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp) has been described. The measurements were carried out using cyclic voltammetry in buffer solution with pH 1. This modified electrode exhibits potent and persistent electroxidation behavior followed by well-separated oxidation peaks towards AA, DA, UA and Trp with increasing of the oxidation current. For the quaternary mixture containing AA, DA, UA and Trp, the 4 compounds can well separate from each other at the scan rate of 100 mVs(-1) with a potential difference of 270 mV, 150 mV and 260 mV for the oxidation peak potentials of AA-DA, DA-UA and UA-Trp, respectively, which was large enough to simultaneous determine AA, DA, UA and Trp. The catalytic peak current obtained, was linearly dependent on the AA, DA, UA and Trp concentrations in the range of 7.77-833 μM, 7.35-833 μM, 0.23-83.3 μM and 0.074-34.5 μM and the detection limits for AA, DA, UA and Trp were 1.11, 1.05, 0.033 and 0.011 μM, respectively. The analytical performance of this sensor has been evaluated for simultaneous detection of AA, DA, UA and Trp in human serum and urine samples.     

Tellurium-nanowire-coated glassy carbon electrodes for selective and sensitive detection of dopamine

Tellurium-nanowire-coated glassy carbon electrodes (TNGCEs) have been fabricated and employed for selective and sensitive detection of dopamine (DA). TNGCEs were prepared by direct deposition of tellurium nanowires, 600 ± 150 nm in length and 16 ± 3 nm in diameter, onto glassy carbon electrodes, which were further coated with Nafion to improve their selectivity and stability. Compared to the GCE, the TNGCE is more electroactive (by approximately 1.9-fold) for DA, and its selectivity toward DA over ascorbic acid (AA) and uric acid (UA) is also greater. By applying differential pulse voltammetry, at a signal-to-noise ratio of 3, the TNGCE provides a limit of detection of 1 nM for DA in the presence of 0.5mM AA and UA. Linearity (R(2)=0.9955) of the oxidation current at 0.19 V against the concentration of DA is found over the range 5 nM-1 μM. TNGCEs have been applied to determine the concentration of dopamine to be 0.59 ± 0.07 μM in PC12 cells.     

Flower-like ZnO decorated polyaniline/reduced graphene oxide nanocomposites for simultaneous determination of dopamine and uric acid

A novel sensor was fabricated by electrochemical deposition of ZnO flower-like/polyaniline nanofiber/reduced graphene oxide nanocomposite (ZnO/PANI/RGO) on glassy carbon electrode (GCE) for direct detection of dopamine (DA) and uric acid (UA) in the presence of fixed concentration of ascorbic acid (AA). Surface morphology and characterization of the modified electrodes were confirmed by field emission scanning microscopy (FE-SEM), X-ray diffraction (XRD), Raman and FT-IR spectroscopies. For individual detection, the linear responses were in the two concentration ranges of 0.001–1 μM and 1–1000 μM with detection limit 0.8 nM (S/N = 3) for DA, and also 0.1–100 μM and 100–1000 μM with detection limit 0.042 μM (S/N = 3) for UA. Simultaneous determination of these species in their mixture solution showed the linear responses in the two concentration ranges of 0.1–90 μM and 90–1000 μM with detection limit 0.017 μM (S/N = 3) for DA and also showed two linear range of 0.5–90 μM and 100–1000 μM with detection limit 0.12 μM (S/N = 3) for UA, with coexistence of 1000 μM AA. The applicability of sensor for the analysis of DA, and UA in dopamine injection solution, human serum and human urine samples was successfully demonstrated.     

Electrochemical sensor for dopamine based on a novel graphene-molecular imprinted polymers composite recognition element

A novel composite of graphene sheets/Congo red-molecular imprinted polymers (GSCR-MIPs) was synthesized through free radical polymerization (FRP) and applied as a molecular recognition element to construct dopamine (DA) electrochemical sensor. The template molecules (DA) were firstly absorbed at the GSCR surface due to their excellent affinity, and subsequently, selective copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) was further achieved at the GSCR surface. Potential scanning was presented to extract DA molecules from the imprinted polymers film, and as a result, DA could be rapidly and completely removed by this way. With regard to the traditional MIPs, the GSCR-MIPs not only possessed a faster desorption and adsorption dynamics, but also exhibited a higher selectivity and binding capacity toward DA molecule. As a consequence, an electrochemical sensor for highly sensitive and selective detection of DA was successfully constructed as demonstration based on the synthesized GSCR-MIPs nanocomposites. Under experimental conditions, selective detection of DA in a linear concentration range of 1.0 × 10(-7)-8.3 × 10(-4)M was obtained, which revealed a lower limit of detection and wider linear response compared to some previously reported DA electrochemical MIPs sensors. The new DA electrochemical sensor based on GSCR-MIPs composites also exhibited excellent repeatability, which expressed as relative standard deviation (RSD) was about 2.50% for 30 repeated analyses of 20 μM DA.     

ZnO–CuxO/polypyrrole nanocomposite modified electrode for simultaneous determination of ascorbic acid,dopamine, and uric acid

Novel zinc oxide (ZnO) nanosheets and copper oxide (Cu_xO, CuO, and Cu₂O) decorated polypyrrole (PPy) nanofibers (ZnO–Cu_xO–PPy) have been successfully fabricated for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The morphology and structure of ZnO–Cu_xO–PPy nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Compared with the bare glassy carbon electrode (GCE), PPy/GCE, Cu_xO–PPy/GCE, and ZnO–PPy/GCE, ZnO–Cu_xO–PPy/GCE exhibits much higher electrocatalytic activities toward the oxidation of AA, DA, and UA with increasing peak currents and decreasing oxidation overpotentials. Cyclic voltammetry (CV) results show that AA, DA, and UA could be detected selectively and sensitively at ZnO–Cu_xO–PPy/GCE with peak-to-peak separation of 150 and 154 mV for AA–DA and DA–UA, respectively. The calibration curves for AA, DA, and UA were obtained in the ranges of 0.2 to 1.0 mM, 0.1 to 130.0 μM, and 0.5 to 70.0 μM, respectively. The lowest detection limits (signal/noise = 3) were 25.0, 0.04, and 0.2 μM for AA, DA, and UA, respectively. With good selectivity and sensitivity, the current method was applied to the determination of DA in injectable medicine and UA in urine samples.     

Electrochemical detection of dopamine using porphyrin-functionalized graphene

A new type of porphyrin-functionalized graphene was synthesized and used for highly selective and sensitive detection of dopamine (DA). The aromatic π-π stacking and electrostatic attraction between positively-charged dopamine and negatively-charged porphyrin-modified graphene can accelerate the electron transfer whereas weakening ascorbic acid (AA) and uric acid (UA) oxidation on the porphyrin-functionalized graphene-modified electrode. Differential pulse voltammetry was used for electrochemical detection, the separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA is about 188 mV, 144 mV and 332 mV, which allows selectively determining DA. The detection limit of DA can be as low as 0.01 μM. More importantly, the sensor we presented can detect DA in the presence of large excess of ascorbic acid and uric acid. With good sensitivity and selectivity, the present method was applied to the determination of DA in real hydrochloride injection sample, human urine and serum samples, respectively, and the results was satisfactory.     

Simultaneous voltammetric detection of dopamine and uric acid at their physiological level in the presence of ascorbic acid using poly(acrylic acid)-multiwalled carbon-nanotube composite-covered glassy-carbon electrode

The use of poly(acrylic acid) (PAA)-multiwalled carbon-nanotubes (MWNTs) composite-coated glassy-carbon disk electrode (GCE) (PAA-MWNTs/GCE) for the simultaneous determination of physiological level dopamine (DA) and uric acid (UA) in the presence of an excess of ascorbic acid (AA) in a pH 7.4 phosphate-buffered solution was proposed. PAA-MWNTs composite was prepared by mixing of MWNTs powder into 1 mg/ml PAA aqueous solution under sonication. GCE surface was modified with PAA-MWNTs film by casting. AA demonstrates no voltammetric peak at PAA-MWNTs/GCE. The PAA-MWNTs composite is of a high surface area and of affinity for DA and UA adsorption. DA exhibits greatly improved electron-transfer rate and is electro-catalyzed at PAA-MWNTs/GCE. Moreover, the electro-catalytic oxidation of UA at PAA-MWNTs/GCE is observed, which makes it possible to detect lower level UA. Therefore, the enhanced electrocatalytic currents for DA and UA were observed. The anodic peak currents at approximately 0.18 V and 0.35 V increase with the increasing concentrations of DA and UA, respectively, which correspond to the voltammetric peaks of DA and UA, respectively. The linear ranges are 40 nM to 3 microM DA and 0.3 microM to 10 microM UA in the presence of 0.3 mM AA. The lowest detection limits (S/N=3) were 20 nM DA and 110 nM UA.     

Simultaneous determination of dopamine, ascorbic acid, and uric acid using carbon ionic liquid electrode

A recently constructed carbon composite electrode using room temperature ionic liquid as pasting binder was employed as a novel electrode for sensitive, simultaneous determination of dopamine (DA), ascorbic acid (AA), and uric acid (UA). The apparent reversibility and kinetics of the electrochemical reaction for DA, AA, and UA found were improved significantly compared to those obtained using a conventional carbon paste electrode. The results show that carbon ionic liquid electrode (CILE) reduces the overpotential of DA, AA, and UA oxidation, without showing any fouling effect due to the deposition of their oxidized products. In the case of DA, the oxidation and reduction peak potentials appear at 210 and 135mV (vs Ag/AgCl, KCl, 3.0M), respectively, and the CILE shows a significantly better reversibility for dopamine. The oxidation peak due to the oxidation of AA occurs at about 60mV. For UA, a sharp oxidation peak at 340mV and a small reduction peak at 250mV are obtained at CILE. Differential pulse voltammetry was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Relative standard deviation for DA, AA, and UA determinations were less than 3.0% and DA, AA, and UA can be determined in the ranges of 2.0x10(-6)-1.5x10(-3), 5.0x10(-5)-7.4x10(-3), and 2.0x10(-6)-2.2x10(-4)M, respectively. The method was applied to the determination of DA, AA, and UA in human blood serum and urine samples.     

A lactate biosensor based on lactate dehydrogenase/nictotinamide adenine dinucleotide (oxidized form) immobilized on a conducting polymer/multiwall carbon nanotube composite film

An amperometric lactate biosensor was developed based on a conducting polymer, poly-5,2′-5′,2′′-terthiophene-3′-carboxylic acid (pTTCA), and multiwall carbon nanotube (MWNT) composite on a gold electrode. Lactate dehydrogenase (LDH) and the oxidized form of nicotinamide adenine dinucleotide (NAD⁺) were subsequently immobilized onto the pTTCA/MWNT composite film. The modified electrode was characterized by quartz crystal microbalance (QCM), scanning electron microscopy (SEM), and electrochemical experiments. The detection signal was amplified by the pTTCA/MWNT assembly onto which a sufficient amount of enzyme was immobilized and stabilized by the covalent bond formation between the amine groups of enzyme and the carboxylic acid groups of the pTTCA/MWNT film. Experimental parameters affecting the sensor responses, such as applied potential, pH, and temperature, were assessed and optimized. Analytical performances and dynamic ranges of the sensor were determined, and the results showed that the sensitivity, stability, and reproducibility of the sensor improved significantly using pTTCA/MWNT composite film. The calibration plot was linear (r² = 0.9995) over the range of 5 to 90 μM. The sensitivity was approximately 0.0106 μA/μM, with a detection limit of 1 μM, based on a signal/noise ratio of 3. The applicability of the sensor for the analysis of l-lactate concentration in commercial milk and human serum samples was demonstrated successfully.     

A novel sensor based on electrochemical polymerization of diglycolic acid for determination of acetaminophen

Diglycolic acid (DA) polymer was coated on glassy carbon (GC) electrode by cyclic voltammetry (CV) technique for the first time. The electrochemical performances of the modified electrode were investigated by CV and electrochemical impedance (EIS). The obtained electrode showed an excellent electrocatalytic activity for the oxidation of acetaminophen (ACOP). A couple of well-defined reversible electrochemical redox peaks were observed on the ploy(DA)/GC electrode in ACOP solution. Compared with bare GC electrode, the oxidation peak potential of ACOP on ploy(DA)/GC electrode moved from 0.289 V to 0.220 V. Meanwhile, the oxidation peak current was much higher on the modified electrode than that on the bare GC electrode, indicating DA polymer modified electrode possessed excellent performance for the oxidation of ACOP. This kind of capability of the modified electrode can be enlisted for the highly sensitive and selective determination of ACOP. Under the optimized conditions, a wide linear range from 2 × 10(-8) to 5.0 × 10(-4)M with a correlation coefficient 0.9995 was obtained. The detection limit was 6.7 × 10(-9)M (at the ratio of signal to noise, S/N=3:1). The modified electrode also exhibited very good stability and reproducibility for the detection of ACOP. The established method was applied to the determination of ACOP in samples. An average recovery of 100.1% was achieved. These results indicated that this method was reliable for determining ACOP.     

Determination of dopamine in the presence of ascorbic acid using poly(3,5-dihydroxy benzoic acid) film modified electrode

A polymerized film of 3,5-dihydroxy benzoic acid (DBA) was prepared on the surface of a glassy carbon electrode (GCE) in neutral solution by cyclic voltammetry (CV). The poly(DBA) film-coated GCE exhibited excellent electrocatalytic activity toward the oxidation of dopamine (DA). A linear range of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M and a detection limit of 6.0 × 10⁻⁸ M were observed in pH 7.4 phosphate buffer solutions. Moreover, the interference of ascorbic acid (AA) was effectively eliminated. This work provides a simple and easy approach to selective detection of DA in the presence of AA.     

A novel electrochemical sensor for determination of dopamine based on AuNPs@SiO(2) core-shell imprinted composite

A novel core-shell composite of gold nanoparticles (AuNPs) and SiO(2) molecularly imprinted polymers (AuNPs@SiO(2)-MIPs) was synthesized through sol-gel technique and applied as a molecular recognition element to construct an electrochemical sensor for determination of dopamine (DA). Compared with previous imprinting recognition, the main advantages of this strategy lie in the introduction and combination of AuNPs and biocompatible porous sol-gel material (SiO(2)). The template molecules (DA) were firstly adsorbed at the AuNPs surface due to their excellent affinity, and subsequently they were further assembled onto the polymer membrane through hydrogen bonds and π-π interactions formed between template molecules and silane monomers. Cyclic voltammetry (CV) was carried out to extract DA molecules from the imprinted membrane, and as a result, DA could be rapidly and effectively removed. The AuNPs@SiO(2)-MIPs was characterized by ultraviolet visible (UV-vis) absorbance spectroscopy, transmission electron microscope (TEM) and Fourier transform infrared spectrometer (FT-IR). The prepared AuNPs@SiO(2)-MIPs sensor exhibited not only high selectivity toward DA in comparison to other interferents, but also a wide linear range over DA concentration from 4.8×10(-8) to 5.0×10(-5)M with a detection limit of 2.0×10(-8)M (S/N=3). Moreover, the new electrochemical sensor was successfully applied to the DA detection in dopamine hydrochloride injection and human urine sample, which proved that it was a versatile sensing tool for the selective detection of DA in real samples.     

Role of vesicle pools in action potential pattern-dependent dopamine overflow in rat striatum in vivo

Action potential (AP) patterns and dopamine (DA) release are known to correlate with rewarding behaviors, but how codes of AP bursts translate into DA release in vivo remains elusive. Here, a given AP pattern was defined by four codes, termed total AP number, frequency, number of AP bursts, and interburst time [N, f, b, i].. The 'burst effect' was calculated by the ratio (γ) of DA overflow by multiple bursts to that of a single burst when total AP number was fixed. By stimulating the medial forebrain bundle using AP codes at either physiological (20 Hz) or supraphysiological (80 Hz) frequencies, we found that DA was released from two kinetically distinct vesicle pools, the fast-releasable pool (FRP) and prolonged-releasable pool (PRP), in striatal dopaminergic terminals in vivo. We examined the effects of vesicle pools on AP-pattern dependent DA overflow and found, with given 'burst codes' [b=8, i=0.5 s], a large total AP number [N = 768, f = 80 Hz] produced a facilitating burst-effect (γ[b8/b1] = 126 ± 3%), while a small total AP number [N=96, 80 Hz] triggered a depressing-burst-effect (γ[b8/b1] = 29 ± 4%). Furthermore, we found that the PRP (but not the FRP) predominantly contributed to the facilitating-burst-effect and the FRP played an important role in the depressing-burst effect. Thus, our results suggest that striatal DA release captures pre-synaptic AP pattern information through different releasable pools.     

A colorimetric detection of dopamine in urine and serum based on the CeO2@ZIF-8/Cu-CDs laccase-like nanozyme activity

This study reports a sensitive and selective colorimetric approach for the analysis of dopamine (DA) based on CeO₂@ZIF-8/Cu-CDs laccase-like nanozymes activity. The CeO₂@ZIF-8/Cu-CDs was synthesized using cerium oxide (CeO₂) and copper-doped carbon dots (Cu-CDs) with 2-methylimidazole by a facilely hydrothermal approach. The CeO₂@ZIF-8/Cu-CDs exhibited excellent laccase-like nanozymes activity and can oxidize the colorless substrate (DA) to red product with 4-aminoantipyrine as the chromogenic agent. The Michaelis–Menten constant (K_m) and the maximal velocity (V_max) of CeO₂@ZIF-8/Cu-CDs are 0.20 mM and 1.48 μM/min, respectively. The detection method has a linear range of 0.05–7.5 μg/mL and a detection limit as low as 8.5 ng/mL with good reproducibility. The developed colorimetric sensor was applied to rapid and precise quantitative evaluation of DA levels in serum and urine samples. This study presents a new approach for detecting biological molecules by utilizing the controlled regulation of nanozymes' laccase-like activity.     

Effects of α-Synuclein Monomers Administration in the Gigantocellular Reticular Nucleus on Neurotransmission in Mouse Model

The aim of the study was to examine the Braak’s hypothesis to explain the spreading and distribution of the neuropathological changes observed in the course of Parkinson’s disease among ascending neuroanatomical regions. We investigated the neurotransmitter levels (monoamines and amino acid concentration) as well as tyrosine hydroxylase (TH) and transglutaminase-2 (TG2) mRNA expression in the mouse striata (ST) after intracerebral α-synuclein (ASN) administration into gigantocellular reticular nucleus (Gi). Male C57BL/10 Tar mice were used in this study. ASN was administrated by stereotactic injection into Gi area (4 μl; 1 μg/μl) and mice were decapitated after 1, 4 or 12 weeks post injection. The neurotransmitters concentration in ST were evaluated using HPLC detection. TH and TG2 mRNA expression were examined by Real-Time PCR method. At 4 and 12 weeks after ASN administration we observed decrease of DA concentration in ST relative to control groups and we found a significantly higher concentration one of the DA metabolites—DOPAC. At these time points, we also noticed the increase in DA turnover determined as DOPAC/DA ratio. Additionally, at 4 and 12 weeks after ASN injection we noted decreasing of TH mRNA expression. Our findings corresponds with the Braak’s theory about the presence of the first neuropathological changes within brainstem and then with time affecting higher neuroanatomical regions. These results obtained after administration of ASN monomers to the Gi area may be useful to explain the pathogenesis of Parkinson’s disease.

     

Electrochemical oxidation behavior of guanine and adenine on graphene–Nafion composite film modified glassy carbon electrode and the simultaneous determination

The electrochemical behavior of guanine and adenine on the graphene and Nafion composite film modified glassy carbon electrode was investigated by differential pulse voltammetry (DPV). The results indicated that the modified electrode exhibited an excellent electrocatalytic activity towards the oxidation of guanine and adenine, testified by the increased oxidation peak current and decreased oxidation potential. The experimental conditions were optimized. The separation of the two oxidation peaks was 0.364 V in 0.1 M pH 4.4 acetate buffer solution (ABS). Based on this, a novel electrochemical method was proposed to simultaneously determine guanine and adenine with the detection limit of 0.58 (guanine) and 0.75 (adenine) μM (S/N = 3). The proposed method was applied to determine guanine and adenine in milk powder, urine and herring sperm DNA samples with satisfactory results. The value of (G + C)/(A + T) in herring sperm DNA was calculated to be 0.8065. The fabricated electrode showed excellent reproducibility, stability and anti-interference.     

ATP microelectrode biosensor for stable long-term in vitro monitoring from gastrointestinal tissue

We have developed a stable and selective ATP biosensor for long-term in vitro tissue monitoring. The electrode was fabricated by entrapping glucose oxidase (GOx) and hexokinase (HEX) in a poly-phenol film on a Pt microelectrode. The biosensor was stable to a fixed concentration of glucose for over 20 min and had a limit of detection of 9.9 ± 3.2 nM, with a sensitivity of 45.8 ± 1.22 pA μM(-1). Most significantly of all, the response on the ATP biosensor did not alter in the presence of 1mM ascorbic acid, 5 μM dopamine, 5 μM serotonin, 5 μM ADP and 5 μM AMP. The ATP biosensor was also shown to have excellent stability over 7 days, and showed only a 23.92 ± 3.55% loss in sensitivity. The ATP biosensor was utilised for the in vitro detection of ATP from gastrointestinal tissue. The ATP biosensor response was stable for 5h during in vitro recordings from ileum tissue. ATP release was shown to be greater from the mucosal surface in the ileum compared to the colon.     

Iridium oxide pH sensor for biomedical applications. Case urea-urease in real urine samples

This work demonstrates the implementation of iridium oxide films (IROF) grown on silicon-based thin-film platinum microelectrodes, their utilization as a pH sensor, and their successful formatting into a urea pH sensor. In this context, Pt electrodes were fabricated on Silicon by using standard photolithography and lift-off procedures and IROF thin films were growth by a dynamic oxidation electrodeposition method (AEIROF). The AEIROF pH sensor reported showed a super-Nerstian (72.9±0.9mV/pH) response between pH 3 and 11, with residual standard deviation of both repeatability and reproducibility below 5%, and resolution of 0.03 pH units. For their application as urea pH sensors, AEIROF electrodes were reversibly modified with urease-coated magnetic microparticles (MP) using a magnet. The urea pH sensor provided fast detection of urea between 78μM and 20mM in saline solution, in sample volumes of just 50μL. The applicability to urea determination in real urine samples is discussed.