Advances in xanthine biosensors and sensors: A review.

Xanthine is derived from hypoxanthine by xanthine oxidase (XOD), a flavoprotein containing molybdenum and non-haem iron, sulfur and from guanine by guanine deaminase enzyme. Xanthine is oxidized into uric acid by XOD. Xanthine is used as an indicator of fish freshness, based on the reactions in which ATP is degraded into xanthine and its quantity increases with time of fish death. Fresh fish meat is required in food industry for making high quality items. The determination of xanthine in biological fluids is also used in diagnosing and curing many diseases like renal failure, gout, xanthinuria, hyperuricemia. Various methods are available for detection of xanthine but most of them are complicated, time consuming less sensitive & specific and require expensive instrumental setup and trained person to operate. Enzyme based biosensors and non enzymic sensors overcome these disadvantages, as these are simple, rapid, specific, sensitive and easy to operate. Present review describes xanthine biosensors, which work optimally between pH 3.5-9.0, temperature 25 °C-65 °C, xanthine concentration ranging from 0.001-50 × 104 µM. These biosensors have also been used to measure xanthine concentration in beverages, urine and serum samples. Various modified electrodes have been discussed for the detection of xanthine using both enzymatic and non-enzymatic approaches in the present review.

A comprehensive review of methods for determination of l-lysine with detailed description of biosensors.

l-lysine being one of the essential amino acids is not produced by the body, but is obtained through diet. l-lysine determination is important in the food and pharmaceutical industries as well as have medical and diagnostic applications. The normal l-lysine levels in a healthy human serum sample is 150 to 250 µmol/l. There is imbalance in l-lysine levels in certain diseased conditions. So, it could be a biomarker for diagnosis. Various basic methods are available for the determination of l-lysine such as colorimetric, radioisotope dilution, chromatographic, fluorometric and voltammetric methods. These methods have certain disadvantages like sample pretreatment, costly, time consuming and requirement of skilled personnel. These drawbacks are overcome by the use of biosensors due to their high sensitivity, stability and specificity. The present review article discusses about the principles, merits and demerits of the various analytic methods for determination of l-lysine with special emphasis on biosensors. l-lysine biosensors work ideally under the optimum pH 5 to 10, potential range -0.05 to 1.5 V, temperature 25 to 40 °C, with linear range 0.01 to 5500 µM, detection limit 0.000004 to 650 µM and response time 2 to 300 s. The sensor had storage stability between 14 and 200 days.

The Prevalence of Polycystic Ovary Syndrome: A Brief Systematic Review.

BACKGROUND: Polycystic ovary syndrome (PCOS), the major endocrinopathy among reproductive-aged women, is not yet perceived as an important health problem in the world. It affects 4%-20% of women of reproductive age worldwide. The prevalence, diagnosis, etiology, management, clinical practices, psychological issues, and prevention are some of the most confusing aspects associated with PCOS. AIM: The exact prevalence figures regarding PCOS are limited and unclear. The aim of this review is to summarize comprehensively the current knowledge on the prevalence of PCOS. MATERIALS AND METHODS: Literature search was performed through PubMed, ScienceDirect, Cochrane Library, and Google Scholar (up to December 2019). All relevant articles published in English language were identified following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. RESULTS: Our analysis yielded 27 surveys with a pooled mean prevalence of 21.27% using different diagnostic criteria. The proportion of women with PCOS also increased in the last decade. CONCLUSION: The current review summarizes and interprets the results of all published prevalence studies and highlights the burden of the syndrome, thereby supporting early identification and prevention of PCOS in order to reverse the persistent upward trend of prevalence.

Preparation, Characterization, and Application of Enzyme Nanoparticles.

Enzymes are fundamental biocatalysts, which regulate various metabolic reactions. They exhibit high substrate specificity, sensitivity, and exceptional catalytic activity under ideal conditions and, hence, have been used as industrial catalysts. Enzyme nanoparticles have attracted the scientific community as they can be used for environment protection, biochemical engineering, and biomedicine. It is necessary to understand the nature of enzyme nanoparticles interactions with their analyte. Various types of enzyme/protein nanoparticles have been immobilized onto a matrix (electrode or membrane) for the fabrication of biosensors. Among the various nanoparticles and nanomaterials, organic nanoparticles have received more attention due to their fascinating properties. Therefore, the future research should be focused to develop advanced biosensors based on enzyme nanoparticles that could be used for early diagnosis and management of chronic diseases. This chapter explains various enzyme nanoparticles-based biosensors, such as GOX, HRP, uricase, cholesterol oxidase, hemoglobin, and their biomedical applications.

Quantitative analysis of hydrogen peroxide with special emphasis on biosensors.

Determination of hydrogen peroxide (H2O2) has become essential in pharmaceutical, biological, clinical and environmental studies. The conventional detection methods of H2O2 such as colourimetry, titration, chromatography, spectrophotometry, fluorimetry, chemiluminescence have limited success, due to their poor selectivity and sensitivity, long analysis time and lack of long-term reliability and reproducibility. The biosensors overcome these limitations because of their simplicity, rapidity, selectivity and high sensitivity. This review describes the principle, analytic parameters, merits and demerits of various methods of H2O2 determination with special emphasis on biosensors. The classification of biosensors based on various materials/nanomaterials and electrodes have been described in detail. The recent advances in vivo sensing and bio-sensing of H2O2 by hemoglobin nanoparticles are also presented. The significant challenges and future perspective for highly selective H2O2 detection are discussed.

Preparation, characterization and application of haemoglobin nanoparticles for detection of acrylamide in processed foods.

The nanoparticles of haemoglobin (HbNPs) were prepared by desolvation method and characterized by transmission electron microscopy (TEM),UV-vis spectroscopy, Fourier transformation infra red (FTIR) spectroscopy and X-ray diffraction (XRD) and atomic force microscopy (AFM). Protein profile of HbNPs was also studied by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). An amperometric acrylamide biosensor was constructed by immobilizing covalently HbNPs onto polycrystalline Au electrode. The Au electrode was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectra (EIS) before and after immobilization of HbNPs. The biosensor showed optimum current response within 2s at 0.26V, pH 5.0 at room temperature (20°C). The biosensor measured the acrylamide concentration in processed foods. The working range of biosensor was 0.1nm-100mM with a limit of detection (LOD) as low as 0.1nM. The biosensor measured acrylamide concentration in various processed foods such as biscuits, bread, potato crisps, "kurkure", nuts and fried cereals. The analytical recovery of added acrylamide in aqueous extract of food at 5 and 10mM was 99% and 98% respectively. Within-and between-batch, co-efficient of variations were 3.85% and 4.67% respectively. The structural analogs of acrylamide such as acrylic acid and propionic acid had practically no interference on the biosensor.

An amperometric H2O2 biosensor based on hemoglobin nanoparticles immobilized on to a gold electrode.

The nanoparticles (NPs) of hemoglobin (Hb) were prepared by desolvation method and characterized by transmission electron microscopy (TEM), UV spectroscopy and Fourier-transform IR (FTIR) spectroscopy. An amperometric H2O2 biosensor was constructed by immobilizing HbNPs covalently on to a polycrystalline Au electrode (AuE). HbNPs/AuE were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) before and after immobilization of HbNPs. The HbNPs/AuE showed optimum response within 2.5 s at pH 6.5 in 0.1 M sodium phosphate buffer (PB) containing 100 µM H2O2 at 30°C, when operated at -0.2 V against Ag/AgCl. The HbNPs/AuE exhibited Vmax of 5.161 ± 0.1 µA cm-2 with apparent Michaelis-Menten constant (Km) of 0.1 ± 0.01 mM. The biosensor showed lower detection limit (1.0 µM), high sensitivity (129 ± 0.25 µA cm-2 mM-1) and wider linear range (1.0-1200 µM) for H2O2 as compared with earlier biosensors. The analytical recoveries of added H2O2 in serum (0.5 and 1.0 µM) were 97.77 and 98.01% respectively, within and between batch coefficients of variation (CV) were 3.16 and 3.36% respectively. There was a good correlation between sera H2O2 values obtained by standard enzymic colorimetric method and the present biosensor (correlation coefficient, R2 =0.99). The biosensor measured H2O2 level in sera of apparently healthy subjects and persons suffering from diabetes type II. The HbNPs/AuE lost 10% of its initial activity after 90 days of regular use, when stored dry at 4°C.

Point of care with micro fluidic paper based device integrated with nano zeolite-graphene oxide nanoflakes for electrochemical sensing of ketamine.

The present study was aimed to develop an ultrasensitive technique for electroanalysis of ketamine; a date rape drug. It involved the fabrication of nano-hybrid based electrochemical micro fluidic paper-based analytical device (EµPADs) for electrochemical sensing of ketamine. A paper chip was developed using zeolites nanoflakes and graphene-oxide nanocrystals (Zeo-GO). EµPAD offers many advantages such as facile approach, economical and potential for commercialization. Nanocrystal modified EµPAD showed wide linear range 0.001-5nM/mL and a very low detection limit of 0.001nM/mL. The developed sensor was tested in real time samples like alcoholic and non-alcoholic drinks and found good correlation (99%). The hyphenation of EµPAD integrated with nanocrystalline Zeo-GO for detection of ketamine has immense prospective for field-testing platforms. An extensive development could be made for industrial translation of this fabricated device.

Determination of lactic acid with special emphasis on biosensing methods: A review.

Lactic acid (2-Hydroxypropanoic acid) is generated from pyruvic acid under anaerobic condition in skeletal muscles, brain, red blood cells, and kidney. Lactate in normal human subjects get cleared very quickly at a rate of 320mmol/L/hr, mostly by liver metabolism and re-conversion of lactate back to pyruvate. Measurement of lactate level in serum is required for the differential diagnosis and medical management of hyperlactatemia, cardiac arrest and resuscitation, sepsis, reduced renal excretion, hypoxia induced cancer, decreased extra hepatic metabolism, intestinal infarction and lactic acidosis. Determination of lactate is also important in dairy products and beverages to access their quality. Among the various methods available for detection of lactate, most are complicated, nonspecific, less sensitive and require time-consuming sample pretreatment, expensive instrumental set-up and trained persons to operate, specifically for chromatographic methods. Biosensing methods overcome these drawbacks, as these are simple, fast, specific and highly sensitive. Lactate biosensors reported so far, work optimally within 3-180s, between pH, 5.5-8.5 and temperature 22°C to 37°C and lactate concentration ranging from 10 to 2000µM. These biosensors have been employed to measure lactate level in embryonic cell culture, beverages, urine, and serum samples and reused upto 200-times within a period of 7-216 days. This review presents the principles, merits and demerits of various analytical methods for lactate determination with special emphasis on lactate biosensors. The future perspective for improvement of analytic performance of lactate biosensors are discussed.

Correlation between chemical components of billary calculi and bile & sera and bile of gallstone patients.

Total cholesterol, total bilirubin, calcium, oxalate, inorganic phosphate, magnesium, iron, copper, sodium and potassium were analyzed quantitatively in gallstones, bile of gall bladder and sera of 200 patients of cholelithiasis (52 cholesterol, 76 mixed and 72 pigment stone patients) and their contents were correlated between calculi and bile and sera and bile in these three type of stone patients. A significant positive correlation was observed between total cholesterol, total bilirubin of calculi and bile, copper of bile and sera of cholesterol stone patients, copper of calculi and bile, total bilirubin, oxalate, magnesium, potassium of sera and bile of pigment stone patients and oxalate and iron of stone and bile, total bilirubin, oxalate, sodium of sera and bile of mixed stone patients. A significant negative correlation was found between magnesium of serum and bile of cholesterol stone patients, oxalate of calculi and bile of pigment stone patients and magnesium of serum and bile of mixed stone patients.

Determination of serum triglycerides using lipase, glycerol kinase, glycerol-3-phosphate oxidase and peroxidase co-immobilized onto alkylamine glass beads.

A method for determination of serum triglycerides (Tgs) using lipase, glycerol kinase, glycerol-3-phosphate oxidase and peroxidase co-immobilized onto alkylamine glass beads (pore diameter 55 nm) through glutaraldehyde coupling was developed and evaluated. The minimum detection limit of the method was 0.54 mM. The analytical recovery of added triolein in the serum was 97.55 +/- 1.5% (mean +/- S.D.). The mean value of serum Tgs, determined by the present method showed a good correlation (r = 0.984) with the Bayer's kit method, employing free enzymes. The within and between batch coefficients of variation (CV) were < 2.25% and < 1.35% respectively. No significant loss of activity was observed, when co-immobilized enzymes were reused for about 200 times and stored at 4 degrees C in distilled water. The cost of Tg determination for 200 serum samples was less, as compared with Bayer's kit method.

Determination of total cholesterol in serum by cholesterol esterase and cholesterol oxidase immobilized and co-immobilized on to arylamine glass.

Commercial cholesterol esterase from bovine pancreas and cholesterol oxidase from Brevibacterium recombinant type have been immobilized individually and co-immobilized on to arylamine glass beads (pore diameter, 55 nm) through diazotization. A method for discrete analysis of total cholesterol in serum was developed employing individually immobilized cholesterol esterase (0.36 mg/50 mg of glass beads) and cholesterol oxidase (0.41 mg/50 mg of glass beads) or co-immobilized cholesterol esterase and cholesterol oxidase (0.56 mg/100 mg of glass beads). Peroxidase from horseradish immobilized on to arylamine glass (0.9 mg/50 mg of glass beads) was common in both the cases. 4-Aminophenazone (0.25 mg/1.5 ml of reaction mixture) and phenol (0.5 mg/1.5 ml of reaction mixture) were used to form dye. In the method, cholesterol ester is hydrolysed by cholesterol esterase to free fatty acid and cholesterol, which is oxidized by cholesterol oxidase to cholestenone and H(2)O(2) x H(2)O(2) is determined enzymically with horseradish peroxidase by additive coupling of 4-aminophenazone with phenol, and the resulting quinoneimine dye is measured at 520 nm, (epsilon=4.0 x 10(-4)). The lower detection limit of the method was 42.8 mg/l for individually immobilized enzymes and 21.4 mg/l for co-immobilized enzymes. Within-day and between-day coefficients of variation were <1.5% and <4.0% respectively for individually immobilized enzymes and <1.0% and <2.5% respectively for co-immobilized enzymes. A good correlation (r=0.99) was found between total serum cholesterol obtained by the present method and a commercial enzo-kit method employing free enzymes. The individually immobilized/co-immobilized enzymes did not show much loss of activity after their 300 uses, when stored at 4 degrees C in distilled water. The co-immobilized enzymes showed better efficiency in terms of sensitivity, linearity and precision compared with individually immobilized enzymes.