Detection Of L-glutamate Research Articles

A modified Prussian blue biosensor with improved stability based on the use of self-assembled monolayers and polydopamine for quantitative L-glutamate detection.

Aminiature L-glutamate (L-Glu)biosensor is describedbased on Prussian blue (PB) modification with improved stability by using self-assembled monolayers (SAMs) technology and polydopamine (PDA). A gold microelectrode (AuME) was immersed in NH2(CH2)6SH-ethanol solution, forming well-defined SAMs via thiol-gold bonding chemistry which increased the number of deposited Prussian blue nanoparticles (PBNPs) and confined them tightly on the AuME surface. Then, dopamine solution was dropped onto the PBNPs surface and self-polymerized into PDA to protect the PB structure from destruction. The PDA/PB/SAMs/AuME showed improved stability through CV measurements in comparison with PB/AuME, PB/SAMs/AuME, and PDA/PB/AuME. The constructed biosensor achieved a high sensitivity of 70.683 nAµM-1cm-2 in the concentrationrange 1-476µM L-Gluwith a low LOD of 0.329µM and performed well in terms of selectivity, reproducibility, and stability. In addition, the developed biosensor was successfully applied to the determination of L-Glu in tomato juice, and the results were in good agreement with that of high-performance liquid chromatography (HPLC). Due to its excellent sensitivity, improved stability, and miniature volume, the developed biosensor not only has a promising potential for application in food sample analysis but also provides a good candidate for monitoring L-Glu level in food production.

Development of highly sensitive, flexible dual L-glutamate and GABA microsensors for in vivo brain sensing

Real-time tracking of neurotransmitter levels in vivo has been technically challenging due to the low spatiotemporal resolution of current methods. Since the imbalance of cortical excitation/inhibition (E:I) ratios are associated with a variety of neurological disorders, accurate monitoring of excitatory and inhibitory neurotransmitter levels is crucial for investigating the underlying neural mechanisms of these conditions. Specifically, levels of the excitatory neurotransmitter L-glutamate, and the inhibitory neurotransmitter GABA, are assumed to play critical roles in the E:I balance. Therefore, in this work, a flexible electrochemical microsensor is developed for real-time simultaneous detection of L-glutamate and GABA. The flexible polyimide substrate was used for easier handling during implantation and measurement, along with less brain damage. Further, by electrochemically depositing Pt-black nanostructures on the sensor’s surface, the active surface area was enhanced for higher sensitivity. This dual neurotransmitter sensor probe was validated under various settings for its performance, including in vitro, ex vivo tests with glutamatergic neuronal cells and in vivo test with anesthetized rats. Additionally, the sensor’s performance has been further investigated in terms of longevity and biocompatibility. Overall, our dual L-glutamate:GABA sensor microprobe has its unique features to enable accurate, real-time, and long-term monitoring of the E:I balance in vivo. Thus, this new tool should aid investigations of neural mechanisms of normal brain function and various neurological disorders.

A biosensor based on oriented immobilization of an engineered l-glutamate oxidase on a screen-printed microchip for detection of l-glutamate in fermentation processes

This paper describes an amperometric biosensor utilizing an engineered l-glutamate oxidase for glutamate monitoring in microbial fermentation processes. We designed a general immobilization strategy that utilized a chitin-binding domain (ChBD-tag) as a biotether to further immobilize l-glutamate oxidase (GLOX) in an oriented manner on a screen-printed Prussian blue nanocube microchip (PB/SPC) with the biopolymer chitosan. The improved l-glutamate biosensor exhibited an enhanced sensitivity of 53.4 µA L mmol−1 cm−2 and a linear range from 25 µmol/L to 300 µmol/L with a detection limit of 9 µmol/L, and retained 95 % of its initial activity after two weeks of usage. In addition, the as-prepared biosensor was applied for real-time monitoring of food ingredient l-glutamate concentration during the fermentation process, which was in good agreement with that of high-performance liquid chromatography (HPLC). Above all, the l-glutamate biosensor prepared by this method had high analytical performance, and could fully realize real-time and high-efficiency monitoring in glutamate fermentation.

A peptide aptamer based electrochemical amperometric sensor for sensitive L-glutamate detection

L-glutamate (L-Glu) has gained much attention owing to its contribution to the umami taste and it plays important roles in the central nervous system. Herein, an enzyme-free amperometric biosensor based on a peptide possessing an electroactive ferrocene linker as ferrocene-Gly-Gly-Gly-Gly-Ile- Pro-Val-Tyr-Cys-Gly-Leu-Ile-Gly-Gly-Gly-Gly-Lys-(CH2)4- thioctic acid self- assembled on gold electrode was designed and fabricated for specific determination of L-Glu. The biosensor was characterised via cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscopy. The biosensor showed optimum response within 200 s at 0.10 V in phosphate-buffered saline. Moreover, the biosensor exhibited excellent sensitivity and a low detection limit of 1.00 × 10−10 M. The sensitivity at an L-Glu concentration of 1.00 × 10−7 M – 1.00 × 10−3 M was 0.1572 μA/M, and that at an L-Glu concentration of 1.00 × 10−10 M – 1.00 × 10−7 M was 0.0293 μA/M. The peptide-based biosensor had excellent specificity and a wider linear range. The relative standard deviation of the L-Glu concentrations measured by the biosensor in a hundred-fold dilution of mouse serum samples was less than 5.00% compared with the high-performance liquid chromatography results, and the recovery rate of L-Glu was from 93.32% to 105.15%.

N,N'-Diphenylthiourea electrochemical sensor for the detection of l-glutamate and Aspartate in beef.

This study was conducted to design an electrochemical sensor for detection of l-glutamate (L-Glu) and Aspartate (Asp), which contribute largely to the umami taste of beef. Using N, N'-diphenylthiourea (DPTU), polypyrrole (PPy), and polyvinyl chloride (PVC), a composite electrode (DPTU/PVC/PPy/Pt) was prepared for rapidly electrochemical detection of l-Glu and Asp. The surface morphology of the synthesized functionalized electrode was characterized by Field Emission Scanning Electron Microscopy (FESEM). Potentials of umami amino acids accounted for 97.8%, while six interferential amino acids existed. The linear correlation between the content of l-Glu and Asp in beef broth was studied under different treatment conditions. The sensor compared with an amino acid analyzer well detected the contents of l-Glu and Asp in beef broths, with a coefficient of 0.991 in Pearson correlation analysis and an accuracy of 88.9%. The proposed electrochemical sensor showed good concurrence with previously reported methods and was effectively employed for the quantification of l- Glu and Asp in beef. PRACTICAL APPLICATION: The sensor exhibits the good performance with high stability and high accuracy. And it is a potential sensing platform with good reproducibility, making the proposed method suitable and reliable for routine analysis of L-Glu and Asp in beef. This method was proved promising for quantitative detecting amino acids in beef.

L-Glutamate biosensor based on l-glutamate oxidase immobilized onto ZnO nanorods/polypyrrole modified pencil graphite electrode

A method is described for the construction of a highly sensitive electrochemical biosensor for the detection of l-glutamate. Such a biosensor is based on immobilization of glutamate oxidase (GluOx) onto zinc oxide nanorods (ZnONRs)/polypyrrole (PPy) composite. This composite was electro-deposited onto a pencil graphite (PG) electrode. The enzyme electrode was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), Fourier transform infra-red spectroscopy (FTIR) and cyclic voltammetry (CV). The biosensor showed optimum response at pH 8.5 (0.1M Tris–HCl buffer) and 30°C, when operated at 20mVs−1. The biosensor exhibited excellent sensitivity (detection limit as 0.18nM), fast response time (less than 5s) and wide linear range (0.02–500μM). Analytical recovery of added l-glutamate (20 and 40μM) in commercial Chinese soup were 95.40 and 97.56% respectively .The within batch and between batch coefficients of variation (CV) in measurement of l-glutamate in commercial Chinese soup were 2.35% and 4.5% respectively. The enzyme electrode lost 30% of its initial activity after 100 uses over a period of 90 days, when stored at 4°C.

The importance of the presence of a 5'-ribonucleotide and the contribution of the T1R1 + T1R3 heterodimer and an additional low-affinity receptor in the taste detection of L-glutamate as assessed psychophysically.

The molecular receptors underlying the purported "umami" taste quality commonly associated with l-glutamate have been controversial. Evidence supports the involvement of the T1R1 + T1R3 heterodimer, a GPCR broadly tuned to l-amino acids, but variants of two mGluRs expressed in taste buds have also been implicated. Using a rigorous psychophysical taste-testing paradigm, we demonstrated impaired, if not eliminated, detection of MSG in WT and T1R1, T1R2, T1R3, and T1R2 + T1R3 KO mice when the contribution of sodium was minimized by the epithelial sodium channel blocker amiloride. When inosine 5'-monophosphate (IMP), a ribonucleotide that potentiates the l-glutamate signal through the T1R1 + T1R3 heterodimer, was added, the WT and T1R2 KO mice were able to detect the compound stimulus across all MSG (+amiloride) concentrations due, in part, to the taste of IMP. In contrast, mice lacking T1R1 or T1R3 could not detect IMP alone, yet some were able to detect MSG + amiloride + IMP, but only at the higher MSG concentrations. Interestingly, the sensitivity of T1R1 KO mice to another l-amino acid, lysine, was unimpaired, suggesting that some l-amino acids can be detected through T1R1 + T1R3-independent receptors without sensitivity loss. Given that IMP is not thought to affect mGluRs, behavioral detection of l-glutamate appears to require the contribution of the T1R1 + T1R3 receptor. However, the partial competence observed in some T1R1 and T1R3 KO mice when MSG + amiloride + IMP was tested suggests that a T1R1 or T1R3 homodimer or an unidentified protein, perhaps in conjunction with T1R1 or T1R3, can serve as a low-affinity taste receptor for l-glutamate in the presence of IMP.

Two continuous coupled assays for ornithine-δ-aminotransferase

We have developed two new continuous coupled assays for ornithine-δ-aminotransferase (OAT) that are more sensitive than previous methods, measure activity in real time, and can be carried out in multiwell plates for convenience and high throughput. The first assay is based on the reduction of Δ1-pyrroline-5-carboxylate (P5C), generated from ornithine by OAT, using human pyrroline 5-carboxylate reductase 1 (PYCR1), which results in the concomitant oxidation of NADH (nicotinamide adenine dinucleotide, reduced form) to NAD+ (nicotinamide adenine dinucleotide, oxidized form). This procedure was found to be three times more sensitive than previous methods and is suitable for the study of small molecules as inhibitors or inactivators of OAT or as a method to determine OAT activity in unknown samples. The second method involves the detection of l-glutamate, produced during the regeneration of the cofactor pyridoxal 5’-phosphate (PLP) of OAT by an unamplified modification of the commercially available Amplex Red l-glutamate detection kit (Life Technologies). This assay is recommended for the determination of the substrate activity of small molecules against OAT; measuring the transformation of l-ornithine at high concentrations by this assay is complicated by the fact that it also acts as a substrate for the l-glutamate oxidase (GluOx) reporter enzyme.

A 1-step microplate method for assessing the substrate range of l-α-amino acid aminotransferase

Aminotransferase enzymes catalyse the reversible substitution of a keto group for an amino group. While this reaction is highly stereoselective with respect to the amino group, each enzyme can usually catalyse the turnover of a number of different substrates. As the substrate range cannot be inferred from the sequence, it remains an early bottleneck when selecting an enzyme for a biocatalysis application. We have developed a simple first round characterisation method applicable to the broad range of aminotransferases that accept l-glutamate, the central junction of cellular transamination, as one of the amino donors. The assay is based on l-glutamate detection by its highly specific dehydrogenase enzyme in a coupled assay, ending in the reduction of the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-tetrazolium-5-carboxanilide (XTT). While products of most tetrazolium salts are water-insoluble, XTT is reduced to a water soluble colored formazan, allowing direct spectrophotometric detection. The reaction is carried out in microplate format using a single endpoint measurement and is thus suitable for automation.The setup was tested with 7 aminotransferase enzymes: Escherichia coli branched chain amino acid aminotransferase, Pseudomonas aeruginosa and Klebsiella pneumoniae aromatic amino acid AT, Bacillus subtilis histidinol-phosphate AT, and Thermus aquaticus aspartate, serine and histidinol-phosphate AT. In addition to 17 of the 20 proteinogenic amino acids, 32 alternative substrates were tested.

Immunogold Detection of L-glutamate and D-serine in Small Synaptic-Like Microvesicles in Adult Hippocampal Astrocytes

Glutamate and the N-methyl-D-aspartate receptor ligand D-serine are putative gliotransmitters. Here, we show by immunogold cytochemistry of the adult hippocampus that glutamate and D-serine accumulate in synaptic-like microvesicles (SLMVs) in the perisynaptic processes of astrocytes. The estimated concentration of fixed glutamate in the astrocytic SLMVs is comparable to that in synaptic vesicles of excitatory nerve terminals (≈ 45 and ≈ 55 mM, respectively), whereas the D-serine level is about 6 mM. The vesicles are organized in small spaced clusters located near the astrocytic plasma membrane. Endoplasmic reticulum is regularly found in close vicinity to SLMVs, suggesting that astrocytes contain functional nanodomains, where a local Ca(2+) increase can trigger release of glutamate and/or D-serine.

Surface Amplification of L-Glutamate Using a Patterned Bienzymatic System for Biosensing Applications

Electronic sensing of neurotransmitter molecules is based on a diffusion-limited process, which requires the immobilization of biological recognition elements as close as possible to the active area of the sensor. Moreover, in many applications, the analyte concentration is very low. In particular, the in situ detection of neurotransmitter release from neurons is challenging due to the limited number of molecules secreted and their fast diffusion and reuptake immediately after release. In this paper, we present a method that allows for the local amplification of L-glutamate directly on the chip surface. Our approach is based on the surface patterning of a bienzymatic system consisting of glutamate oxidase (GLOD) and glutamic-pyruvate transaminase (GPT) that amplifies L-glutamate via a recycling process. The surface chemistry was optimized for maximal enzyme loading. The level of amplification was determined using a colorimetric assay. Coimmobilization of GLOD and GPT yielded at least a doubling of the signal, and increasing the surface concentrations of each enzyme led to amplification levels that approached those obtained in solution. We show that these enzymes can be patterned on substrates using a flip chip bonder for aligned microcontact printing. Furthermore, primary mouse hippocampal neurons were successfully cultured on these patterned surfaces and remained viable for at least five days. The enzymatic pattern was preserved on the substrate surface for the same time period. Lastly, amplification of L-glutamate released from neurons seven days in vitro was detected. Thus, we conclude that this bienzymatic system can ultimately be applied to biosensor surfaces for the in vitro detection of L-glutamate.

Coulometric Detection of Components in Liquid Plugs by Microfabricated Flow Channel and Electrode Structures

Coulometry has been demonstrated to be effective for determining the analyte in a liquid plug on the nanoliter-scale confined in a flow channel. A plug prepared in a rhombus structure of an auxiliary flow channel was placed on a thin-film three-electrode system, and hydrogen peroxide was detected as a model analyte. Under a fixed potential, the current decayed rapidly, particularly in shallow flow channels, thus making reproducible amperometric detection difficult. On the other hand, the increasing charge during coulometry facilitated the measurements. A constricted flow channel structure with an array of platinum strips for the working electrode was effective at efficiently consuming the analyte to improve the sensitivity and lower the detection limit. Compared to the case of a single short working electrode with the same area, a 4-fold increase in sensitivity was observed for the best combination of flow channel height and interstrip distance. With an increase in the generated current while maintaining the background at a low level, the detection limit was lowered from 1.3 μM to 410 nM using working electrodes with the same area. Furthermore, the processing of solutions containing L-glutamate or L-glutamate oxidase and the detection of L-glutamate were demonstrated.

Differential Photoluminescent and Electrochemiluminescent Detection of Anions with a Modified Ruthenium(II)–Bipyridyl Complex

A new guanidinium 3,3'-functionalized bipyridylruthenium(II) complex has been prepared for the differential sensing of L-glutamate and dihydrogenphosphate anions depending on the luminescent detection scheme. The effects of such anions on the photoluminescent (PL) and electrochemiluminescent (ECL) properties of the complex have been investigated and compared. The PL intensity increases up to fourfold in the presence of L-glutamate. The increase of intensity in the presence of dihydrogenphosphate is weaker and no change in PL intensity is observed in presence of acetate, iodide, or chloride anions. With n-tripropylamine, ECL emission of the Ru(II) complex is initiated at 1.45 V versus Ag/AgCl/KCl and the ECL intensity increases only in the presence of dihydrogenphosphate. Indeed, L-glutamate is already oxidized at the relatively high potential required for ECL generation and thus it does not affect the ECL signal. The comparison of the competitive ECL and PL assays in a mixture of anions confirms the differential detection of L-glutamate and of dihydrogenphosphate. Thus, both sensing channels (i.e., PL and ECL) show different selectivities depending on the nature and on the electroactivity of the target anions. Multianion analysis is demonstrated in competitive assays using complementary detection methods.

A stable and selective electrochemical biosensor for the liver enzyme alanine aminotransferase (ALT)

An electrochemical method to determine alanine aminotransferase (ALT) activity over its normal and elevated physiological range was developed based upon detection of l-glutamate at a glutamate oxidase-modified platinum electrode. Measurements were carried out in the presence of ALT co-substrates l-alanine and α-ketoglutarate and current response from either the oxidation of hydrogen peroxide or the re-oxidation of the mediator ferrocene carboxylic acid was employed. The enzyme electrode was tested over a 6-month period and found to retain 79% of its original activity towards ALT detection with >200 measurements performed over this time. Signals associated with interfering electroactive species (ascorbic acid and uric acid) were eliminated using background subtraction at a denatured glutamate oxidase enzyme electrode. The sensitivity of the device was found to be 0.845 nA U −1 L ALT with t 90 = 180 s, linear range 10–1000 U L −1 and LOD of 3.29 U L −1 using amperometry at E app = 0.4 V vs. Ag/AgCl at 308 K (35 °C).

Ferrocene Functionalized Single-Walled Carbon Nanotube Bundles. Hybrid Interdigitated Construction Film for l-Glutamate Detection

A ferrocene functionalized SWCNT noncovalent nanohybrid was investigated by using a ferrocene/SWCNT interdigitated construction film as an electrode for l-glutamate detection. Ferrocene could immobilize on the surface of SWCNT bundles, and the ferrocene/SWCNT hybrid had a high stability not only in water but also in an organic solvent such as ethanol and acetone (no sediment was observed for more than 3 months). The nanohybrid could not only be thoroughly dispersed in ethanol but also adhere tightly onto glass substrates to form an interdigitated construction film. Owing to the existence of more carbon nanotubes, more active electrochemical mediators, and the unique interdigitated structure of the film, the ferrocene/SWCNT electrode exhibited a high catalytic efficiency, high sensitivity, and fast response during the detection of a low concentration of l-glutamate (1 μM). A good linear relationship between current and concentration was obtained from 1 to 7 μM.

Simultaneous detection of l-glutamate and nitric oxide from adherently growing cells at known distance using disk shaped dual electrodes

An ex vivo system for simultaneous detection of nitric oxide (NO) and l-glutamate using integrated dual 250 μm platinum disk electrodes modified individually with suitable sensing chemistries has been developed. One of the sensors was coated with an electrocatalytic layer of Ni tetrasulfonate phthalocyanine tetrasodium salt (Ni-TSPc) covered by second layer of Nafion, which stabilises on the one hand the primary oxidation product NO + and prevents interferences from negatively charged compounds such as NO 2 −. For glutamate determination, the second electrode was modified with a crosslinked redox hydrogel consisting of Os complex modified poly(vinylimidazol), glutamate oxidase and peroxidase. A manual x– y– z micromanipulator on top of an inverted optical microscope was used to position the dual electrode sensor at a defined distance of 5 μm from a cell population under visual control. C6 glioma cells were stimulated simultaneously with bradykinin or VEGF to release NO while KCl was used to invoke glutamate release. For evaluation of the glutamate sensors, in some experiments HN10 cells were used. To investigate the sensitivity and reliability of the system, several drugs were applied to the cells, e.g. Ca 2+-channel inhibitors for testing Ca 2+-dependence of the release of NO and glutamate, rotenone for inducing oxidative stress and glutamate antagonists for analysing glutamate release. With these drugs the NO and glutamate release was modulated in a similar way then expected from previously described systems or even in-vivo measurements. We therefore conclude that our system is suitable to analyse stress-induced mechanisms in cell lines.

Specific detection of l-glutamate in food using flow-injection analysis and enzymatic recycling of substrate

A flow injection analysis (FIA) system for specific determination of l-glutamate in food samples based on a bi-enzymatic amplification system has been developed. The content of l-glutamate in the sample was amplified by cycling between l-glutamate dehydrogenase (GlDH) and a novel enzyme, d-phenylglycine aminotransferase ( d-PhgAT). In this system, GlDH converts l-glutamate to 2-oxoglutarate with concomitant reduction of NAD + to NADH. d-PhgAT transfers an amino group from d-4-hydroxyphenylglycine to 2-oxoglutarate, thus recycling l-glutamate. Accumulation of NADH in the course of the enzymatic recycling was monitored both by fluorescence and UV absorbance and used for quantification of l-glutamate. The assay was characterized by high long-term stability (at least 70 days) and good reproducibility (within-day and between-day RSDs were 4.3–7.3% and 8.9%). The fluorimetric assay was slightly more sensitive with a l-glutamate detection limit of 0.4 μM and linear range of 2.5–50 μM. The assay was specific for l-glutamate, with recoveries between 95–103% in the presence of 17 different amino acids tested one by one. The method was applied to analysis of real food samples and results were correlated with a commercial Boehringer Mannheim assay kit.

Selective detection of l-glutamate using a microfluidic device integrated with an enzyme-modified pre-reactor and an electrochemical detector

A microfluidic device integrated with a nanoliter volume enzyme pre-reactor and an enzyme-modified electrode was developed for the highly selective continuous measurement of glutamate (Glu). The device consists mainly of two glass plates. One plate incorporates an electrochemical cell that consists of working electrode (WE), reference electrode (RE) and counter electrode (CE). The WE is modified with a bilayer film of Os-polyvinylpyrridine-based mediator containing horseradish peroxidase (Os-gel-HRP). The WE was operated at −50 mV versus Ag. The other plate has a thin layer flow channel integrated with a pre-reactor. The reactor has a number of micropillars (20 μm in diameter, 20 μm high and separated from each other by a 20 μm gap) modified with ascorbate oxidase (AAOx) to eliminate l-ascorbic acid (AA). The enzymatic oxidation of AA is superior to that obtained with our previously reported pre-electrolysis type micro-reactor since electrochemically reversible transmitters such as catecholamines do not provide a cathodic current at the WE. In addition, the high operation potential of the pre-reactor causes unknown electroactive species, which also cause interference at the detection electrode. As a result, we were able to detect 1 μM Glu continuously at a low flow rate even when AA concentration was 100 μM.

A glass capillary microelectrode based on capillarity and its application to the detection of L-glutamate release from mouse brain slices.

A new glass capillary microelectrode for L-glutamate is described using pulled glass capillaries (tip size, approximately 12.5 microm) with a very small volume (approximately 2 microl) of inner solution containing glutamate oxidase (GluOx) and ascorbate oxidase. The operation of the electrode is based on capillary action that samples L-glutamate into the inner solution. The enzyme reaction by GluOx generates hydrogen peroxide that is detected at an Os-gel-HRP polymer modified Pt electrode in a three-electrode configuration. The amperometric response behavior of the electrode was characterized in terms of the capillarity, response time, sensitivity and selectivity for measurements of L-glutamate. The currents at 0 V vs. Ag/AgCl increased linearly with the L-glutamate concentration from 10 to 150 microM for in vitro and in situ calibrations. The response was highly selective to L-glutamate over ascorbate, dopamine, serotonin and other amino acids. The detection of L-glutamate in the extracellular fluids of different regions of mouse hippocampal slices under stimulation of KCl was demonstrated.

Combined imaging and chemical sensing of l-glutamate release from the foregut plexus of the Lepidopteran, Manduca sexta

A new combined imaging and chemical detection sensor for the measurement of localized l-glutamate release at the insect neuromuscular junction (NMJ) is presented. The sensor is comprised of an l-glutamate-sensitive fluorescent gel, spin-coated onto the tip of an optical imaging fiber. The gel is composed of l-glutamate oxidase (GLOD); a pH-sensitive fluorescent dye, SNAFL; and poly(acrylamide- co- N-acryloxysuccinimide) (PAN). NH 3 is liberated from the interaction of l-glutamate with GLOD, which reversibly reduces the emitted fluorescence signal from SNAFL. This sensor has a spatial resolution of 3–4 μm, and an l-glutamate detection limit of between 10 and 100 μM. l-glutamate release and re-uptake from the foregut plexus of Manduca sexta was detected by the sensor in the presence of the l-glutamate re-uptake blocker dihydrokainate, and the post-synaptic l-glutamate receptor antagonist CNQX.