This paper describes the preparation of and experimentation undertaken by heterogeneous chitosan membrane as ion selective electrode for glutamate ion. The linearity response was obtained in the range of 1.0x10(-5) to 1.0x10(-1)M with a detection limit of 1.0x10(-6)M. The performance of the electrode was found in the pH range of 4.0-8.0 at temperature 25+/-3 degrees C. The response time was at 5-35s and was useful for a period of more than 4 months. The selectivity values towards some anions indicates good selectivity over a number of interfering anions. No significant improvement of membrane performance over additional of plasticizers such as 2-NPOE, BEHA and DOPP. The electrodes gave sufficient Nernstian responses with the exception of membrane with 2-NPOE.
The electrochemical biosensors based on poly(o-phenylenediamine) (PoPD) and acetylcholinesterase (AChE) and choline oxidase (ChO) enzymes were fabricated on carbon fibre (CF) substrate. The electropolymerized PoPD was used to reduce the interfering substances. The electrode assembly was completed by depositing functionalized carbon nano tubes (FCNTs) and Nafion (Naf). Amperometric detection of acetylcholine (ACh) and choline (Ch) were realized at an applied potential of +750 mV vs Ag/AgCl (saturated KCl). At pH 7.4, the final assembly, Naf-FCNTs/AChE-ChO((10:1))/PoPD/CF(Elip), was observed to have high sensitivity towards Ch (6.3±0.3 μA mM(-1)) and ACh (5.8±0.3 μA mM(-1)), linear range for Ch (K(M)=0.52±0.03 mM) and ACh (K(M)=0.59±0.07 mM), and for Ch the highest ascorbic acid blocking capacity (97.2±2 1mM AA). It had a response time of <5s and with 0.045 μM limit of detection. Studies on different ratio (ACh/Ch) revealed that 10:1, gave best overall response.
A non-enzymatic glucose sensor of multi-walled carbon nanotube-ruthenium oxide/composite paste electrode (MWCNT-RuO(2)/CPE) was developed. The electrode was characterized by using XRD, SEM, TEM and EIS. Meanwhile, cyclic voltammetry and amperometry were used to check on the performances of the MWCNT-RuO(2)/CPE towards glucose. The proposed electrode has displayed a synergistic effect of RuO(2) and MWCNT on the electrocatalytic oxidation of glucose in 3M NaOH. This was possible via the formation of transitions of two redox pairs, viz. Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI). A linear range of 0.5-50mM glucose and a limit of detection of 33 μM glucose (S/N=3) were observed. There was no significant interference observable from the traditional interferences, viz. ascorbic acid and uric acid. Indeed, results so obtained have indicated that the developed MWCNT-RuO(2)/CPE would pave the way for a better future to glucose sensor development as its fabrication was without the use of any enzyme.
The nickel (Ni) nanocrystals (average diameter 9.7+/-2.3nm) were deposited onto composite graphite electrode from a plating solution of 5.0mM NiCl(2)6H(2)O and 1.0M NH(4)Cl using scan rate of 6500mVs(-1). The initial potential -1.5V and final potential -0.5V vs. Ag/AgCl with applied time 120s were used for the whole deposition process. The variations of applied overpotentials and deposition times have affected the characteristics of Ni nanocrystals. It was found that the structural formation of Ni nanocrystals obtained were almost pure hexagonal close-packed (hcp). This study has demonstrated that the tuning of the final size, morphology and structural formation of the Ni nanocrystal were affected by control of nucleation, growth and hydrogen evolution processes in fast scan voltammetry technique used.
A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.
A flow injection analysis (FIA) incorporating a thiosemicarbazone-based coated wire electrode (CWE) was developed method for the determination of mercury(II). A 0.1 M KNO(3) carrier stream with pH between 1 and 5 and flow rate of 1 mL·min(-1) were used as optimum parameters. A linear plot within the concentration range of 5 × 10(-6)–0.1 M Hg(II), slope of 27.8 ± 1 mV per decade and correlation coefficient (R2) of 0.984 were obtained. The system was successfully applied for the determination of mercury(II) in dental amalgam solutions and spiked environmental water samples. Highly reproducible measurements with relative standard deviation (RSD < 1% (n = 3)) were obtained, giving a typical throughput of 30 samples·h(-1).
This paper discusses the application of a reagentless, selective microbiosensor as a useful alternative tool for monitoring D-serine in neural samples. The main components of the 125-μm-diameter disk biosensor were D-amino acid oxidase for D-serine sensitivity (linear region slope, 61 ± 7 μA cm(-2) mM(-1); limit of detection, 20 nM), and poly-phenylenediamine for rejection of electroactive interference. The response time of the biosensor was of the order of 1 s, ideal for 'real-time' monitoring, and detection of systemically administered D-serine in brain extracellular fluid is demonstrated. Exploitation of this probe might resolve queries involving regulation of D-serine in excitotoxicity, and modulation of N-methyl-D-aspartate receptor function by D-serine and glycine in the central nervous system.
A new poly(4-vinyl pyridine) (P4VP) based cadmium (Cd)-ion selective electrode (ISE) was developed. The 4-vinyl pyridine (4VP) was first polymerized electrochemically on the surface of graphite, later characterized by FTIR, SEM/EDX and then optimized as ISE for Cd. At optimal pH 6.4, slope of 27.7±0.8mVdecade(-1), linear concentration range of 1×10(-7) to 1.0×10(-1)M Cd(2+) and limit of detection (S/N=3) of 2.51×10(-8)M were obtained. The ISE was very selective towards Cd(2+), with K(pot)<1×10(-2) in the presence of the usual cations and anions in water samples. Response time and shelf life of less than 1min and 90 days, respectively, were observed. Its application was tested in various types of samples.
The mechanisms involving insulin and anti-hypertensive drugs regulation for in vivo cerebral glucose metabolism are not well-understood. This might be due to lack of direct means of measuring cerebral glucose. It is known that the continuous delivery of glucose to the brain is critical for its normal metabolic function. In this study, we report the effect of insulin and anti-hypertensive drugs on glucose level in the striatum of rats. The rats were divided into two groups, i.e. hyperglycemia (14.8+/-0.3mM plasma glucose) and diabetic (10.8+/-0.2mM plasma glucose). A custom-built glucose microsensor was implanted at coordinates A/P 1.0 from bregma, M/L +2.5 and D/V -5.0 (from dura) in the striatum. The amperometric response obtained at +0.23 V vs. Ag|AgCl corresponded to the glucose level in striatum. By varying the concentrations of protaminc zinc insulin infused into the rats, striatum glucose level was found to remain constant throughout, i.e. 9.8+/-0.1 and 4.7+/-0.1mM for hyperglycemic rats and for diabetic rats, respectively. However, infusion of valsartan and felodipine has lowered the striatum glucose level significantly. These findings agreed with the hypothesis that suggested striatum glucose uptake do not depend on insulin but is clearly dependant on anti-hypertensive drugs administration.
This study aimed to evaluate the significant extraction factors in achieving higher recovery yield of total polyphenols, phenolic acids and flavonoids content from Citrus limon peel using two-level factorial design. The effect of five independent factors including drying temperature (40-60 °C), methanol concentration (20-60%), extraction temperature (28-60 °C), extraction time (30-60 min) and storage duration (0-14 days) were evaluated. Among all the examined factors, results showed that drying temperature, storage duration and extraction temperature were the most significant and contributing factors affecting the total polyphenols, phenolic acids and flavonoids content of lemon peel at P
Endogenous endophthalmitis is rare but sight-threatening in leukemic patients, which can have devastating sequelae. We report a case of a 15-year-old teenager with acute myeloid leukemia on relapse, presented with a mixed picture of endogenous endophthalmitis. The diagnosis dilemma in this patient proved difficult as Investigations and management can be challenging as young teenagers are usually less cooperative than adults. Endogenous endophthalmitis is not uncommon in this group of patients; however, mixed clinical pictures are almost unheard of, and the final diagnosis can be misleading if not treated accordingly. Viral infections such as cytomegalovirus (CMV), bacterial, and fungal are all considered potential opportunistic infections. Diagnosis of endogenous endophthalmitis is complex and relies heavily on the clinical characteristics of each organism supported by intravitreal tapping and culture samples. However, data from endogenous endophthalmitis in leukemic patients is scarce nowadays across the board. In this case report, we highlight the challenges of managing endogenous endophthalmitis in a young leukemic patient due for bone marrow transplantation. Future studies are needed to investigate the current microorganism trends and treatments available. An algorithm for managing endophthalmitis in immunosuppressed patients should be done to provide a better approach from the get-go.
We report the manifestations of vitamin A deficiency (VAD) in three children with underlying autism of different stages. These children were under developmental paediatrician follow-up for autism, and the VAD was not detected until these children presented to Ophthalmology screening for varying stages of signs and symptoms. On further assessment, all of our patients have VAD secondary to poor dietary intake, as autistic patients are associated with having selective eating habits. In our case series, we discuss the spectrum of xerophthalmia presentations, which can be mild and can manifest as punctate epithelial erosions to the more blinding complications at the advanced stage of the disease, mainly irreversible optic neuropathy. The primary management is to address the dietary routine coupled with systemic administration of vitamin A.
D-serine has been implicated as a brain messenger, promoting not only neuronal signalling but also synaptic plasticity. Thus, a sensitive tool for D-serine monitoring in brain is required to understand the mechanisms of D-serine release from glia cells. A biosensor for direct fixed potential amperometric monitoring of D-serine incorporating mammalian D-amino acid oxidase (DAAO) immobilized on a Nafion coated poly-ortho-phenylenediamine (PPD) modified Pt-Ir disk electrode was therefore developed. The combined layers of PPD and Nafion enhanced the enzyme activity and biosensor efficiency by approximately 2-fold compared with each individual layer. A steady state response time (t(90%)) of 0.7+/-0.1s (n=8) and limit of detection 20+/-1 nM (n=8) were obtained. Cylindrical geometry showed lower sensitivity compared to disk geometry (61+/-7 microA cm(-2) mM(-1), (n=4), R(2)=0.999). Interference by ascorbic acid (AA), the main interference species in the central nervous system and other neurochemical electroactive molecules was negligible. Implantation of the electrode and microinjection of D-serine into rat brain striatal extracellular fluid demonstrated that the electrode was capable of detecting D-serine in brain tissue in vivo.
A new implantable electrocatalytic glucose sensor for subcutaneous glucose monitoring has been fabricated by immobilizing glucose oxidase on a chemically modified carbon fiber. The sensor was inserted subcutaneously on a male spraguely rat without any incision after dipping the microsensor in the rat's serum for 3 days. The so called "stained" microsensor, operated in the amperometric mode with an applied potential of +0.23 V versus Ag|AgCl, was able to directly measure the glucose concentration upon infusion of glucose. The results obtained were encouraging, with the response time was less than 2s and the apparent Michaelis-Menten value at 5.1+/-0.5mM. The "stained" microsensor shows good stability and reproducibility with constant response spanned over 25 days. Most common interferences in glucose analysis were minimized by the outerlayer Nafion. Hematology examinations showed minimal material-tissue interaction. Use of such mechanical devices will allow a more refined understanding towards glucose control in diabetic patients as the implanted microsensor was not effected by biocompatibility failures.
A novel glassy carbon electrode (GCE) modified with a composite film of poly (4-vinylpyridine) (P4VP) and multiwalled carbon nanotubes (P4VP/MWCNT GCE) was used for the voltammetric determination of paracetamol (PCT). This novel electrode displayed a combined effect of P4VP and MWCNT on the electro-oxidation of PCT in a solution of phosphate buffer at pH 7. Hence, conducting properties of P4VP along with the remarkable physical properties of MWCNTs might have combined effects in enhancing the kinetics of PCT oxidation. The P4VP/MWCNT GCE has also demonstrated excellent electrochemical activity toward PCT oxidation compared to that with bare GCE and MWCNT GCE. The anodic peak currents of PCT on the P4VP/MWCNT GCE were about 300 fold higher than that of the non-modified electrodes. By applying differential pulse voltammetry technique under optimized experimental conditions, a good linear ratio of oxidation peak currents and concentrations of PCT over the range of 0.02-450 μM with a limit of detection of 1.69 nM were achieved. This novel electrode was stable for more than 60 days and reproducible responses were obtained at 99% of the initial current of PCT without any influence of physiologically common interferences such as ascorbic acid and uric acid. The application of this electrode to determine PCT in tablets and urine samples was proposed.