A microchip sensor for calcium determination

Abstract

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca(2+) ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g(-1) polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca(2+) determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 x 10(-5) - 5.71 x 10(-4) M Ca(2+), with a limit of detection (LOD) of 2.68 x 10(-5) M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results.

Rapid Determination of Calcium in Milk and Water Samples by Reflectance Spectroscopy

“…The limit of detection (LOD) of Ca(II), defined as the concentration equivalent to a signal of blank plus three times the standard deviation of the blank, was calculated to be 0.15 mg⋅L -1 in the low concentration range of linearity. The sensitivity of the proposed method in terms of lowering the LOD of Ca-sensing was better than those of recent analog sensors manufactured by Caglar et al [12] and Malcik et al [13]. The proposed sensing method was validated against flame-AAS analysis of known complex samples of Ca.…”

“…Accordingly, the addition of KCN to the medium is not needed. In various samples assayed with a sensor [12][13][14], Mg(II) at concentrations exceeding 4-to 5-fold was reported to interfere with the determination of calcium. On the other hand, with the proposed technique, Mg(II) was shown not to interfere even at 100-fold (by wt.)…”

“…Recently, a few reports have appeared on the development of optical sensors for calcium ion sensing. Immobilized arsenazo III [12,13], chlorophosphonazo III [14], and amine-containing calcium green derivative [15] in various matrices were used for molecular spectroscopic calcium sensing based on reflectance [12], absorbance [13,14] and fluorescence [15] mesurements. A number of Ca(II) membrane sensors based on different ion carriers have also been reported [16][17][18][19][20][21][22][23].…”

“…[13] were rather high, and remain to be a challenge to be further lowered for applications requiring higher sensitivity. Moreover, in all the mentioned studies, the magnesium tolerance of the sensor was 4-or 5-fold of the amount of calcium being determined [12][13][14], and an increase in Ca/Mg selectivity is required in new sensors. The proposed sensor has been designed to cope with all these inadequacies.…”

Detection of Copper Ion with Laser-Induced Fluorescence in a Capillary Electrophoresis Microchip

“…Compared with electrochemical detectors, optical detectors are more sensitive and reproducible. Different optical methods were also employed in microchips to detect metal ions, including absorbance (Malcik et al 2005;Du et al 2005), reflectance (Caglar et al 2006), chemiluminescence (Liu et al 2003), photodiode array detection (Collins and Lu 2001), and colorimetric methods (Deng and Collins 2003). Currently, the most sensitive optical detection method is based on Laser-induced Fluorescence (LIF) (Xu, Li, and Weber 2007).…”