Strong near-infrared upconversion luminescence of the Er3+/Y3+ co-doped YbVO4 phosphor for multimode optical temperature measurement.

This study explored the enhancement of near-infrared emissions in YbVO4: Er3+ through Y3+ ion doping under a 980 nm laser excitation. The phosphor exhibits weak green emissions at 527 nm (2H11/2 â†’ 4I15/2) and 553 nm (4S3/2 â†’ 4I15/2), red emissions at 654 nm (4F9/2 â†’ 4I15/2), and a strong near-infrared emission at 803 nm (4I9/2 â†’ 4I15/2). Optimal doping concentration of Y3+ ion in YbVO4: 0.02 Er3+ was determined to be 0.1, resulting in a 7.6-fold enhancement of near-infrared luminescence. This enhancement is attributed to defect bands facilitating energy transfer from green and red levels to the near-infrared levels. Furthermore, a multi-mode temperature sensor based on YbVO4: Er3+/Y3+ was developed, offering four distinct temperature sensing modes: TCEL of 2H11/2/4S3/2, NTCEL of 2H11/2/4F9/2 and 4S3/2/4F9/2, and single luminescence emission intensity of 4I9/2 energy level. The sensor demonstrates maximum relative sensitivities of 1.17 % K-1 at 298 K, 0.66 % K-1 at 298 K, 0.41 % K-1 at 298 K and 1.29 % K-1 at 673 K. YbVO4: Er3+/Y3+ phosphor exhibits high temperature sensitivity, showcasing significant potential for optical temperature sensing applications.

Glucose oxidase immobilized in alginate/layered double hydroxides hybrid membrane and its biosensing application.

A new type of amperometric glucose biosensor based on alginate (Alg)/layered double hydroxides (LDHs) organic-inorganic composite film is described. This hybrid material combines the advantages of an organic biopolymer, Alg and inorganic LDHs. Glucose oxidase (GOD) immobilized in the material maintained its activity. The composite films were characterized by UV-Vis. The results indicated that GOD retained the essential feature of its native structure in the composite film. The Alg/LDHs/GOD-modified platinum electrode exhibited a fast response to glucose (achieve 95% of the maximum in 10 s), which provided a linear response to glucose over a concentration range of 1.6 x 10(-5)-2 x 10(-3) M with a detection limit of 4 x 10(-5) M based on S/N = 3. Furthermore, the biosensor exhibited excellent long-term stability, and satisfactory reproducibility. It retained 87% of its original activity after being used for 28 days.

Studies on direct electron transfer and biocatalytic properties of hemoglobin in polyacrylonitrile matrix.

The direct electrochemistry of hemoglobin (Hb) immobilized in polyacrylonitrile (PAN) modified glassy carbon electrode was described. The protein-PAN film exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple in a pH 7.0 phosphate buffer. The formal potential of Hb heme Fe(III)/Fe(II) couple varied linearly with the increase of pH in the range of 5.0-9.0 with a slope of 54 mV pH(-1), which implied that a proton transfer was accompanied with each electron transfer in the electrochemical reaction. Position of Soret absorption band of Hb-PAN film suggested that the Hb kept its secondary structure similar to its native state in the PAN matrix. The Hb in PAN matrix acted as a biologic catalyst to catalyze the reduction of hydrogen peroxide. The electrocatalytic response showed a linear dependence on the H(2)O(2) concentration ranging from 8.3 x 10(-6) to 5 x 10(-4) mol L(-1) with a detection limit of 8.3 x 10(-6) mol L(-1) at 3 sigma. The apparent Michaelis-Menten constant K(M)(app) for H(2)O(2) sensor was estimated to be 0.9 mmol L(-1).

Inhibitive detection of benzoic acid using a novel phenols biosensor based on polyaniline-polyacrylonitrile composite matrix.

A novel sensitive and stable phenols amperometric biosensor, based on polyaniline-polyacrylonitrile composite matrix, was applied for determination of benzoic acid. The electrochemical biosensor functioning was based on the inhibition effect of benzoic acid on the biocatalytic activity of the polyphenol oxidase (PPO) to its substrate (catechol) in 0.1M phosphate buffer solution (pH 6.5). A potential value of -50 mV versus SCE, and a constant catechol concentration of 20 microM were selective to carry out the amperometric inhibition measurement. The kinetic parameters Michaelis-Menten constant (K(M)(app)) and maximum current (I(max)) in the absence and in the presence of benzoic acid were also evaluated and the possible inhibition mechanism was deduced. The inhibiting action of benzoic acid on the polyphenol oxidase electrode was reversible and of the typical competitive type, with an apparent inhibition constant of 38 microM. This proposed biosensor detected levels of benzoic acid as low as 2x10(-7)M in solution. In addition, the effects of temperature, pH value of solution on the inhibition and the interferences were investigated and discussed herein. Inhibition studies revealed that the proposed electrochemical biosensor was applicable for monitoring benzoic acid in real sample such as milk, yoghurt, sprite and cola.