Abdul Lawal

This study assessed concentrations of volatile organic compounds (VOCs) and heavy metals in twelve (12) cosmetic products: medicated powder; talcum powder brands 1, 2, 3, 4, 5, lipstick bands 1, 2, 3 and nail paint brands 1, 2 and 3 manufactured in Nigeria. Except nail paints 1, 2 and 3 which were acidic, other products were alkaline. None of them had the pH suitable for skin suggesting that they could significantly affect the functions of the skin. Fe, Zn, Cu, Cr, Cd and Pb were present in the products. Their presence especially Cr, Cd and Pb which have no biological uses raises questions about the safety of the products. Formaldehyde, toluene, trichloroethene and tetrachloroethene were all present in the cosmetic products analyzed. High concentrations of formaldehyde and toluene especially in the lipsticks and nail paints call for concern because they are carcinogenic and neurotoxic. There is need to have standards for heavy metals and VOCs in cosmetic products to ascertain their ...

This review summarises the most recent contributions in the fabrication of graphene-based electrochemical biosensors in recent years. It discusses the synthesis and application of graphene to the fabrication of graphene-based electrochemical sensors, its analytical performance and future prospects. An increasing number of reviews and publications involving graphene sensors have been reported ever since the first design of graphene electrochemical biosensor. The large surface area and good electrical conductivity of graphene allow it to act as an "electron wire" between the redox centres of an enzyme or protein and an electrode's surface, which make it a very excellent material for the design of electrochemical biosensors. Graphene promotes the different rapid electron transfers that facilitate accurate and selective detection of cytochrome-c, β-nicotinamide adenine dinucleotide, haemoglobin, biomolecules such as glucose, cholesterol, ascorbic acid, uric acid, dopamine and hydrogen peroxide.

Vapour phase polymerisation (VPP) is a well established technique in which the monomer is introduced to an oxidant-coated substrate in vapour form. Polymerisation then takes place at the oxidant vapour interface. VPP is a technique that could be used to immobilise materials to the modified electrode surface. This review article concentrates on the VPP of conducting polymers such as Polypyrrole (PPy) polythiophen (PT) and polyaniline (PANi). VPP of conducting polymers and other non-conducting polymers have extensively been investigated. This review article is divided into three main parts as given in Table of contents related to the VPP process of some important conducting polymers such as PPy, PT, PANi and Poly(3,4-ethylenedioxythiophene). A total of 181 references are cited in this review article and it attempts to look into VPP from inception of the method till present day.

This review covers the progress made in the development of sensors for inorganic and organic phosphates that are significant pollutants within the environmental and biological systems. Phosphate sensors in the forms of amperometric, potentiometric enzyme electrodes, plant tissue electrode and screen printed electrode are described. Instrumental probes such as fluorescence, chemiluminescence, luminescence and potentiometric ion selective electrodes are also described. Recent efforts on the use of voltammetric, potentiometric and amperometric biosensors for the determination of phosphate are highlighted.

A phosphate biosensor based on potentiometric detection mode is described. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were immobilised into polypyrrole films for potentiometric measurement of phosphate in 0.05M barbitone buffer (pH 7.8) which contain 10mM inosine. A minimum detectable amount of 1.0μM phosphate and a linear concentration range of 5–25μM were achieved enabling sensitive potentiometric detection and a wide linear concentration range. The presence of uric and ascorbic acids had the least effect on the performance of the PPy–PNP–XOD–Fe(CN)64− biosensor and therefore will not have any effect on phosphate measurement at levels normally present in water.

The preparation and performance of xanthine oxidase electrochemical biosensor developed for the determination of hypoxanthine is reported. Xanthine oxidase (XOD) and a mediator potassium ferrocyanide (K4Fe(CN) were entrapped into a polypyrrole (PPy) film during galvanostatic film formation. The optimum conditions for the formation of PPy-XOD-Fe(CN)64− film include 0.4M pyrrole, 6.2U/mL XOD, 40mMK4Fe(CN)6, polymerisation period of 200s, and an applied current

The development of two phosphate biosensors is described and compared for potentiometric detection of phosphate. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilised by chemical cross-linking with glutaraldehyde (GLA) and bovine serum albumin (BSA), and via entrapment into polypyrrole (PPy) films by galvanostatic polymerisation. The BSA-GLA film was made with 4.5% v/v GLA and 6.8% w/v BSA with a drying time of 30 min, while polypyrrole entrapment was achieved with 0.5M pyrrole by using a polymerisation time of 200s. A mole ratio of 1:8 (6.2U/mL XOD: 49.6 U/mL PNP) was used for both methods of enzyme immobilisation. Sensitive potentiometric measurements obtained for phosphate with the BSA-GLA-PNP-XOD biosensor were compared with those of PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor. A minimum detectable concentration of 0.1mg/L phosphate and a linear concentration range of 0.5-2.5mg/L were achieved with the PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor. In comparison, a minimum detectable concentration of 2mg/L and a linear concentration range of 4-12 mg/L were achieved with the BSA-GLA immobilisation. The presence of uric and ascorbic acids had the least effect on the performance of the PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor, but will not have any effect on phosphate measurement with both biosensors at levels normally present in water.

ABSTRACT This study examined the influence of microbial contamination on the antioxidant composition and free radical scavenging effects of fresh and decaying spices: Lycopersicon esculentum, Capsicum frutescens S, Capsicum frutescens T and Capsicum annum used by food vendors. Microbial load was enumerated with potato dextrose agar (PDA) using the pour plate technique, phytochemical components were determined using Folio-Ciocalteu, Aluminium chloride, acetone-hexane methods for phenolic, flavonoids and β-carotene & lycopene respectively while free radical scavenging capacity was determined using DPPH method. Decaying L. esculentum had highest microbial population of 7.14 X 105 cfu/g and fresh C. annum had the lowest microbial population of 0.72 X 101cfu/g. Microbial population in decaying spices were generally significantly higher than fresh spices. Aspergillus spp were found in all decaying spices and in fresh C. frutescens T. Microsporum spp were found in all fresh spices except in C. frutescens T and in decaying spices except in C. annum. There were significant decreases (p <0.05) in phenolic, flavonoid, β-carotene and free radical scavenging capacity contents of all decaying spices compared to fresh spices except for phenolic content in C. annum while significant decrease (p < 0.05) in lycopene content was obtained for only decaying L. esculentum compared to fresh one. Reduction in antioxidant activity and phytochemical contents could not be unconnected with the high microbial population in decaying spices because antioxidant activity and phytochemical contents significantly correlate with antibacterial activity. Thus, consumption of decaying spices as shown by our study could pose a serious health challenges due to the presence of high number of microbes detected and loss of healthprotecting ability of the spices.