Search

Glutamate sensors based on the immobilization of glutamate oxidase (GlutOx) were prepared by adsorption on electrodeposited chitosan (Method 1) and by crosslinking with glutaraldehyde (Method 2) on micromachined platinum microelectrodes. It was observed that glutamate sensors prepared by Method 1 have faster response time (

The method for selective enzyme immobilization on arrayed microelectrodes has been investigated in order to fabricate a near-real time biosensor for potential ex vivo or in vivo applications ( e.g. in fermentation processes, in neuroscience studies, etc. ). In this study, chitosan is used as the enzyme immobilization material, permselective polymers (polypyrrole and Nafion ® ) are used as the exclusion layers for charged interferents, and glutamate oxidase is used as the model enzyme for immobilization. To fabricate a glutamate sensor in the array, glutamate oxidase is selectively immobilized on a microelectrode site which is closely arrayed to other microelectrodes (platinum microelectrodes with ∼100 μm separation) with the electrode dimension of ∼30 μm × 140 μm by adsorbing the enzyme on the electrodeposited chitosan matrix on the electrode surface. When testing the glutamate sensor with glutamate at physiological concentrations, it has a linear detection range up to 217 μM, a response time ∼1 s, a limit of detection 2.5 ± 1.2 μM, and a sensitivity 38.1 ± 5.4 nA/μM cm 2 ( n = 8); on the other hand, the closely arrayed control sensor without the chitosan film showed no signal upon the addition of glutamate. Little interferent current was observed. The sensor can retain up to 70% of its initial sensitivity for at least 9 days and no observable decrease in sensor sensitivity was detected after 20 times of continuous operations. Successful selective glutamate oxidase immobilization on closely packed microelectrodes for monitoring glutamate is demonstrated.

In this study, a miniaturized biosensor based on permselective polymer layers (overoxidized polypyrrole (Ppy) and Nafion(®)) modified and enzyme (glutamate oxidase (GlutOx)) immobilized micro-platinum wire electrode for the detection of alanine aminotransferase (ALT) was fabricated. The proposed ALT biosensor was measured electrochemically by constant potential amperometry at +0.7 V vs. Ag/AgCl. The ALT biosensor provides fast response time (~5 s) and superior selectivity towards ALT against both negatively and positively charged species (e.g., ascorbic acid (AA) and dopamine (DA), respectively). The detection range of the ALT biosensor is found to be 10-900 U/L which covers the range of normal ALT levels presented in the serum and the detection limit and sensitivity are found to be 8.48 U/L and 0.059 nA/(U/L·mm²) (N = 10), respectively. We also found that one-day storage of the ALT biosensor at -20 °C right after the sensor being fabricated can enhance the sensor sensitivity (1.74 times higher than that of the sensor stored at 4 °C). The ALT biosensor is stable after eight weeks of storage at -20 °C. The sensor was tested in spiked ALT samples (ALT activities: 20, 200, 400, and 900 U/L) and reasonable recoveries (70%~107%) were obtained.

A sensitive and selective amperometric glutamate microsensor with fast response time (< 5 s) was developed by fabricating a ferrocene/ glutamate oxidase/ Nafion/ polypyrrol (Fc/GlutOx/Nf/Ppy) composite on the micromachined platinum (Pt) microelectrode. The ferrocene-bovine serum albumin (Fc-BSA) conjugate was immobilized on the GlutOx/Nf/Ppy composite of the sensor by physical adsorption. The sensor sensitivity of the Fc-modified glutamate sensor was more than two times higher than that of the control sensor (glutamate sensor without Fc). The Fc modified glutamate microsensor was able to detect glutamate with a wide detection range (up to 540 μΜ) with a low detection limit at 1.35 μΜ. The sensor selectivity towards glutamate against interferents increased significantly after the modification of Pt microelectrodes with Ppy and Nf. The interferent responses from ascorbic acid (AA) and dopamine (DA) were

An implantable, micromachined microprobe with a microsensor array for combined monitoring of the neurotransmitters, glutamate (Glut) and dopamine (DA), by constant potential amperometry has been created and characterized. Microprobe studies in vitro revealed Glut and DA microsensor sensitivities of 126 ± 5 nA μM −1 cm −2 and 3250 ± 50 nA μM −1 cm −2 , respectively, with corresponding detection limits of 2.1 ± 0.2 μM and 62 ± 8 nM, both at comparable ∼1 s response times. No diffusional interaction of H 2 O 2 among arrayed microelectrodes was observed. Also, no responses from the electroactive interferents, ascorbic acid (AA), uric acid (UA), DOPA (a DA catabolite) or DOPAC (a DA precursor), over their respective physiological concentration ranges, were detected. The dual sensing microbe attributes of size, detection limit, sensitivity, response time and selectivity make it attractive for combined sensing of Glut and DA in vivo .

The ability to make rapid, informed decisions about whether or not to engage in a sequence of actions to earn reward is essential for survival. Modeling in rodents has demonstrated a critical role for the basolateral amygdala (BLA) in such reward-seeking actions, but the precise neurochemical underpinnings are not well understood. Taking advantage of recent advancements in biosensor technologies, we made spatially discrete near-real-time extracellular recordings of the major excitatory transmitter, glutamate, in the BLA of rats performing a self-paced lever-pressing sequence task for sucrose reward. This allowed us to detect rapid transient fluctuations in extracellular BLA glutamate time-locked to action performance. These glutamate transients tended to precede lever-pressing actions and were markedly increased in frequency when rats were engaged in such reward-seeking actions. Based on muscimol and tetrodotoxin microinfusions, these glutamate transients appeared to originate from the terminals of neurons with cell bodies in the orbital frontal cortex. Importantly, glutamate transient amplitude and frequency fluctuated with the value of the earned reward and positively predicted lever-pressing rate. Such novel rapid glutamate recordings during instrumental performance identify a role for glutamatergic signaling within the BLA in instrumental reward-seeking actions.

A convenient homogeneous enzyme immunoassay for estradiol is described. Unlike heterogeneous immunoassays, which require time-consuming separation steps or expensive automated systems, homogeneous immunoassays, wherein all reagents are freely suspended in bulk solution, can be simple and fast without costly instrumentation. The key component of this assay system, an estradiol-reporter enzyme conjugate, was prepared by covalently binding β-estradiol-6-(O-carboxymethyl)oxime to glucose-6-phosphate dehydrogenase (G6PDH) by an N-hydroxysuccinimide-enhanced, carbodiimide-mediated coupling reaction. The estradiol-G6PDH activity can be repressed up to 46% upon anti-estradiol antibody binding. The lower detection limit of the assay is 1 nM estradiol in aqueous solution, and the standard curve is linear on logit-log scale-up to 6.7 µM estradiol. A detection limit of 11.5 nM in estradiol-spiked human serum samples suggests the feasibility of applying this assay to monitor estradiol levels for the prediction and prevention of ovarian hyperstimulation syndrome.