Interaction of the human antimicrobial peptide LL-37 with lipid monolayers has been investigated by a range of complementary techniques including pressure-area isotherms, insertion assay, epifluorescence microscopy, and synchrotron x-ray scattering, to analyze its mechanism of action. Lipid monolayers were formed at the air-liquid interface to mimic the surface of the bacterial cell wall and the outer leaflet of erythrocyte cell membrane by using phosphatidylglycerol (DPPG), phosphatidylcholine (DPPC), and phosphatidylethanolamine (DPPE) lipids. LL-37 is found to readily insert into DPPG monolayers, disrupting their structure and thus indicating bactericidal action. In contrast, DPPC and DPPE monolayers remained virtually unaffected by LL-37, demonstrating its nonhemolytic activity and lipid discrimination. Specular x-ray reflectivity data yielded considerable differences in layer thickness and electron-density profile after addition of the peptide to DPPG monolayers, but little change was seen after peptide injection when probing monolayers composed of DPPC and DPPE. Grazing incidence x-ray diffraction demonstrated significant peptide insertion and lateral packing order disruption of the DPPG monolayer by LL-37 insertion. Epifluorescence microscopy data support these findings.

To measure creatinine, electrochemical techniques have been coupled with a range of biological recognition elements in a variety of sensor configurations. (To listen to a podcast about this feature, please go to the Analytical Chemistry website at pubs.acs.org/ac.The measurement of creatinine levels in human blood or urine is clinically essential because the levels partially reflect the state of renal and muscle function. Creatinine is naturally produced by the body and is filtered from the bloodstream by the kidneys in relatively constant amounts every day. The normal physiological concentration is 40-150 µM, but it can exceed 1000 µM in certain pathological conditions. Blood levels >150 µM indicate the need to perform tests such as creatinine clearance. Values >500 µM indicate severe renal impairment, ultimately leading to dialysis or transplantation; 1 levels <40 µM indicate decreased muscle mass.The methods most often used for the clinical determination of creatinine are based on colorimetry. 2 However, the methods are affected by numerous metabolites and drugs found in biological samples, such as glucose, fructose, ketone bodies, ascorbic acid, and cephalosporins. 3,4 Introducing enzymes has increased specificity, but the methods also became complicated and less reliable. Large and expensive benchtop analyzers incorporating a number of electrochemical electrodes have been used in central clinical laboratories. Portable and handheld devices incorporating a single-use creatinine biosensor cartridge also have been used.The goal of biosensor engineering in the clinical laboratory setting is to reduce cost, time, and complexity of routine analysis of biological fluids; to enable near-patient testing of blood, urine, and saliva in medical centers; and ultimately to enable home testing by individuals. 5 This article looks at the developments in electrochemical creatinine biosensor research in terms of sensor design and analytical performance on the basis of the recognition element and the nature of transducer. Parameters and specific performance characteristics to consider include cost (<$10/ sensing strip), response time (<1.5 minutes [min]), detection limit (e10 µM), linear range (10-1000 µM), and lifetime (>1 year).

Magnesium zirconium phosphate, MgZr4P6O24 (MZP) is a magnesium ion conducting ceramic material with potential for application as solid electrolyte in high temperature electrochemical sensor in non-ferrous scrap metal refining and virgin metal alloying operations. In this work, MZP was synthesised using a simple but novel and economical solgel route at a significantly reduced temperature. An insight into the calcination process, and possible phase transformation at higher temperature was obtained using simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Phase identification of the synthesised material was studied after calcining the powder at 900 o C for 3h using X-ray diffraction (XRD); a single monoclinic phase was observed at that temperature. However, a trace amount of possible minor second phase; zirconium oxide phosphate [Zr2(PO4)2O] was formed a T 1000 o C. Impedance spectroscopy measurement on platinised sintered-MZP pellets were carried out in the frequency range 100 mHz 32 MHz and in a temperature range of 30 -800 o C to determine the electrical properties of MZP. Ionic conductivity of MZP was found to be equal to 7.23x10 -3 -1 cm -1 at relatively lower, 725 o C. Furthermore, the Nyquist and modulus plots measured at 764 o C and 390 o C shows single semi-circles suggesting contribution from only grain interiors (GIs). The ionhopping rate was calculated by fitting the conductance spectra to the power law variation, ac dc A n . The ac and dc conductivity of MZP show Arrhenius-type of behaviour with activation energie Ea V SEM f the fractured MZP pellet sintered at 1300 o C for 24h revealed a highly dense microstructure with clearly visible grain boundaries and low porosity which is in good agreement with the relative density of ~99% determined A structure. EDS confirms the presence of Mg, Zr, P, O in appropriate atomic ratio to yield MgZr4P6O24. Finally, TEM on MZP particles with crystallite size of ~50nm also confirmed MZP as stable at 900 o C with no observable second phase, Zr2(PO4)2O.

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