Light-addressable Potentiometric Sensor Research Articles

A LAPS-Based Differential Sensor for Parallelized Metabolism Monitoring of Various Bacteria.

Monitoring the cellular metabolism of bacteria in (bio)fermentation processes is crucial to control and steer them, and to prevent undesired disturbances linked to metabolically inactive microorganisms. In this context, cell-based biosensors can play an important role to improve the quality and increase the yield of such processes. This work describes the simultaneous analysis of the metabolic behavior of three different types of bacteria by means of a differential light-addressable potentiometric sensor (LAPS) set-up. The study includes Lactobacillus brevis, Corynebacterium glutamicum, and Escherichia coli, which are often applied in fermentation processes in bioreactors. Differential measurements were carried out to compensate undesirable influences such as sensor signal drift, and pH value variation during the measurements. Furthermore, calibration curves of the cellular metabolism were established as a function of the glucose concentration or cell number variation with all three model microorganisms. In this context, simultaneous (bio)sensing with the multi-organism LAPS-based set-up can open new possibilities for a cost-effective, rapid detection of the extracellular acidification of bacteria on a single sensor chip. It can be applied to evaluate the metabolic response of bacteria populations in a (bio)fermentation process, for instance, in the biogas fermentation process.

Modeling of the Return Current in a Light-Addressable Potentiometric Sensor.

A light-addressable potentiometric sensor (LAPS) is a chemical sensor with a field-effect structure based on semiconductor. Its response to the analyte concentration is read out in the form of a photocurrent generated by illuminating the semiconductor with a modulated light beam. As stated in its name, a LAPS is capable of spatially resolved measurement using a scanning light beam. Recently, it has been pointed out that a part of the signal current is lost by the return current due to capacitive coupling between the solution and the semiconductor, which may seriously affect the sensor performance such as the signal-to-noise ratio, the spatial resolution, and the sensitivity. In this study, a circuit model for the return current is proposed to study its dependence on various parameters such as the diameter of contact area, the modulation frequency, the specific conductivity of the solution, and the series resistance of the circuit. It is suggested that minimization of the series resistance of the circuit is of utmost importance in order to avoid the influence of the return current. The results of calculation based on this model are compared with experimental results, and its applicability and limitation are discussed.

Modulated light-activated electrochemistry at silicon functionalized with metal-organic frameworks towards addressable DNA chips

Modulated light-activated electrochemistry (MLAE) at semiconductor/liquid interfaces derived from light-addressable potentiometric sensor (LAPS) and light-activated electrochemistry (LAE) for addressable photoelectrochemical sensing has been proposed as a new sensor platform. In this system, a bias voltage is applied to create a depletion layer at the silicon/electrolyte interface. Meanwhile, intensity-modulated light illuminates the movable electrode to generate electron/hole pairs and causes a detectable local AC photocurrent. The AC measurement showed a higher signal-to-noise ratio (SNR) of photocurrents compared to the traditional DC response, while a steeper photocurrent-voltage (I-V) curve than that of LAPS with an insulating layer was obtained. Furthermore, to stabilize and functionalize the silicon substrate, metal-organic framework (MOF) nanoparticles were grown in-situ on the silicon electrode. The successful modification was validated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The AC photocurrent increased as a result of the adsorption of negatively charged DNA, which contributed to the enhancement of the cathodic reduction process at the semiconductor electrodes, indicating a different response mechanism of MLAE from LAPS. The results obtained demonstrate the potential of MOF functionalized MLAE as a robust platform for light-addressable DNA chips with high sensitivity and specificity.

Recent Developments of High-Resolution Chemical Imaging Systems Based on Light-Addressable Potentiometric Sensors (LAPSs).

A light-addressable potentiometric sensor (LAPS) is a semiconductor electrochemical sensor based on the field-effect which detects the variation of the Nernst potential on the sensor surface, and the measurement area is defined by illumination. Thanks to its light-addressability feature, an LAPS-based chemical imaging sensor system can be developed, which can visualize the two-dimensional distribution of chemical species on the sensor surface. This sensor system has been used for the analysis of reactions and diffusions in various biochemical samples. In this review, the LAPS system set-up, including the sensor construction, sensing and substrate materials, modulated light and various measurement modes of the sensor systems are described. The recently developed technologies and the affecting factors, especially regarding the spatial resolution and temporal resolution are discussed and summarized, and the advantages and limitations of these technologies are illustrated. Finally, the further applications of LAPS-based chemical imaging sensors are discussed, where the combination with microfluidic devices is promising.

Effects of 3-dimensional porous graphene oxide network on solid-state sensors

The three-dimensional porous graphene networks (3DPGN) is recently developed graphene material. They possess both the highest mobility of graphene material and the increased surface areas possessed by the porous micro 3D structure. These powerful graphene materials have been exploited to be super-capacitors, batteries, biomedical sensors and other bioengineering applications. In this work, their foundational functions for solid-state sensors are examined with the use of 3D porous graphene oxide (GO) network (3DPGON) as proof-of-concept. Its effects on the classical glass-chemical-electrodes (GCEs) and the pH-sensing light addressable potentiometric sensor are examined, respectively. It is found that the peak currents of 3DPGON film coated GCEs are increased with the increased 3DPGON, while the LAPS’ responding for pH are lowered. The increased currents of GCE are attributed to the enhanced electron transfer (ET) by GO and the enlarged surface area by micro-porous structure. While the lowered pH responding of LAPS is caused by the screen effect induced by 3DPGON coating. In conclusion, the decoration of 3DPGON on solid-state sensors should be considered seriously, it can enhance the total amount of charges exchanging at the liquid-solid interface which is propitious to forming solid-state sensor, but the drawback of 3DPGON modification does exist because the original surface sensing sites may be covered.

Microfluidic chip system integrated with light addressable potentiometric sensor (LAPS) for real-time extracellular acidification detection

Metabolism is a common biological mechanism in living cells. Acidification plays an important role in cell metabolism, in which the extracellular pH change is used to indicate the vitality of cells. For extracellular detection of cell metabolic substances, light addressable potentiometric sensor (LAPS) has many advantages, such as high sensitivity, easy encapsulation, and convenient integration with microfluidic system for cell experiments. LAPS is a spatially resolved biochemical sensor based on field-effect. In this work, we present a microfluidic system integrated with LAPS for real-time extracellular acidification rate (ECAR) detection. The functions of traditional microphysiometer are achieved with simpler structure devices. Polydimethylsiloxane (PDMS) chamber was manufactured for cell culture, and microfluidic flow paths were used for medium and drug delivery. A bubble trap device was applied to eliminate air bubbles generated in microfluidics. Characteristic tests and cell metabolism experiments were carried out to determine the performance of LAPS by monitoring the pH change of hepatoma HepG2 cells. Glucose and doxorubicin were delivered to the cell chamber to verify the effects of the drug. The pH sensitivity of LAPS is 335.5 nA/pH at the working point in constant voltage mode. The ECAR of HepG2 cells was -48.53 mpH/min in normal glucose medium (25 mM), and it changed to -114.42 mpH/min in high glucose medium (125 mM) and -17.88 mpH/min under the effect of doxorubicin (10 μM). The results show that the microfluidic LAPS presents good performance in real-time detection of cell acidification and provides a convenient means of assessing cellular specificity of drugs. The modular structure and high expandability make the microfluidic LAPS has good potential in the application of organ-on-chip.

Effect of Plasma Treatment on the Sensor Properties of a Light‐Addressable Potentiometric Sensor (LAPS)

A light‐addressable potentiometric sensor (LAPS) is a field‐effect‐based (bio‐) chemical sensor, in which a desired sensing area on the sensor surface can be defined by illumination. Light addressability can be used to visualize the concentration and spatial distribution of the target molecules, e.g., H+ ions. This unique feature has great potential for the label‐free imaging of the metabolic activity of living organisms. The cultivation of those organisms needs specially tailored surface properties of the sensor. O2 plasma treatment is an attractive and promising tool for rapid surface engineering. However, the potential impacts of the technique are carefully investigated for the sensors that suffer from plasma‐induced damage. Herein, a LAPS with a Ta2O5 pH‐sensitive surface is successfully patterned by plasma treatment, and its effects are investigated by contact angle and scanning LAPS measurements. The plasma duration of 30 s (30 W) is found to be the threshold value, where excessive wettability begins. Furthermore, this treatment approach causes moderate plasma‐induced damage, which can be reduced by thermal annealing (10 min at 300 °C). These findings provide a useful guideline to support future studies, where the LAPS surface is desired to be more hydrophilic by O2 plasma treatment.

Meso-tetra(4-carboxyphenyl)porphine-Enhanced DNA Methylation Sensing Interface on a Light-Addressable Potentiometric Sensor.

DNA methylation (DNAm) sensors are an emerging branch in the discipline of sensors. It is believed to be able to promote the next generation of epigenetics-based diagnostic technology. Differing from the traditional biochemical sensors that aimed at individual molecules, the challenge in DNAm sensors is how to determine the amount of 5-methylcytosine (5mC) in a continuous nucleotide sequence. Here, we report a comparative study about meso-tetra(4-carboxyphenyl)porphine (TCPP)-based DNAm sensing interfaces on a light-addressable potentiometric sensor (LAPS), depending on TCPP’s postures that are flat in the π-conjugated TCPP layer on reduced-graphene-oxide-decorated LAPS (#1) and stand-up in the covalently anchored TCPP on glutaraldehyde (GA)-treated LAPS (#2), along with the blank one (only GA-treated LAPS, #3). These DNAm sensing interfaces are also distinct from the traditional biosensing interface on LAPS, that is: it is not functionalized by the sensing indicator (5mC antibody, in this case) but by the target nucleotide sequence. The surface characterization techniques such as Raman spectra, scanning electron microscopy, and X-ray photoelectron spectroscopy are conducted to prove the decorations, as well as the anchored nucleotides. It is found that, though all of them can detect as low as one 5mC in the target sequence, the enhanced DNAm sensitivity is obtained by #2, which is evidenced by the higher output-voltage changing ratio for the 5mC site of #2 than those of #1 and #3. Furthermore, the underlying causes for the improved sensitivity in #2 are proposed, according to the conformational and electronic properties of TCPP molecules. Conclusively, TCPP’s synergetic function, including the molecular configuration and the activate (carboxyl) groups on its peripheral substituents, to improve the DNAm sensing interface on LAPS is investigated and demonstrated. This can shed light on a new approach for DNA methylation detection, with the merits of low cost, independence on bisulfite conversion, and polymerase chain reaction.

Thin-film light-addressable potentiometric sensor with SnOx as a photosensitive semiconductor

In this study, a tin-based oxide (SnOx) semiconductor layer on a commercial indium tin oxide (ITO)/glass substrate was investigated for the first time for use as the active layer of a light-addressable potentiometric sensor (LAPS). The photoabsorption of SnOx layers sputtered using varying Ar/O2 gas flow ratios was characterized by means of the ultraviolet–visible spectroscopy (UV–Vis); the photo/electric response of a LAPS directly covered with an NbOx sensing membrane was evaluated under modulated ultraviolet illumination. In situ substrate heating at 250 °C during sputtering and post-deposition rapid thermal annealing (RTA) with temperatures of 400 and 450 °C in a N2 environment were applied to study sample behavior. Based on X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results, the fabricated SnO2 layer can be transformed into a polycrystalline SnO2 phase in the bulk with a surface SnO layer by thermal budget. A high photocurrent and an acceptable pH sensitivity of 1.29 μA and 57.6 mV/pH, respectively, are obtained under UV light-emitting diode (LED) illumination for a LAPS built using a SnOx layer sputtered with a flow ratio of Ar/O2 = 46/4 with substrate heating at 250 °C. The stability and lifetime performance of the SnOx LAPS needs to be improved by further process optimization, especially in terms of developing a crack-free SnOx process and increasing sensing membrane coverage. The experimental results show the potential of SnOx for use as the active layer in a LAPS.

Quantitative differential monitoring of the metabolic activity of Corynebacterium glutamicum cultures utilizing a light-addressable potentiometric sensor system

Applying biosensors for evaluation of the extracellular acidification of microorganisms in various biotechnological fermentation processes is on demand. An early stage detection of disturbances in the production line would avoid costly interventions related to metabolically inactive microorganisms. Furthermore, the determination of the number of living cells through cell plating procedure after cultivations is known as time- and material-consuming. In this work, a differential light-addressable potentiometric sensor (LAPS) system was developed to monitor the metabolic activity of Corynebacterium glutamicum (C. glutamicum ATCC13032) as typical microorganism in fermentation processes. In this context, the number of living cells in suspensions was directly determined utilizing the read-out principle of the LAPS system. The planar sensor surface of the LAPS design allows to fixate 3D-printed multi-chamber structures, which enables differential measurements. In this way, undesirable external influences such as pH variations of the medium and sensor signal drift can be compensated.

A light-addressable microfluidic device for label-free functional assays of bioengineered taste receptor cells via extracellular recording

The functional assay of chemical sensitive cells is of great importance for the preparation of sensitive elements towards the development of cell-based biosensors for chemical sensing. In this study, a novel light-addressable microfluidic device was developed by the integration of a light-addressable potentiometric sensor (LAPS) with a microfluidic chip for label-free functional assays of bioengineered taste receptor cells via extracellular recording. Extracellular potential changes of single bioengineered cells were recorded by LAPS. Microfluidic chip was capable of providing stable microenvironments for cell measurements with a well-defined concentration stimulus. Bioengineered taste receptor cells were utilized as a model of chemical sensitive cells and functional assayed by this light-addressable microfluidic device using bitter stimulation. The results indicate that this microfluidic device can efficiently monitor the membrane potential changes originated from bioengineered taste receptor cells in response to specific bitter stimulation. The bioengineered cells with responsive functions can be easily identified via the analysis on the firing rates of extracellular recording data. The expression of bitter receptors in the bioengineered taste receptor cells was further validated by the immunofluorescent staining results, which proved that the expression of specific bitter receptor was the main contribution to the responsive function of bioengineered cells. This microfluidic device can not only be used for the functional assays of chemical sensitive cells towards chemical sensing, but also suitable to be applied for the research on the chemical signal transduction mechanisms.

Research progress of organoids-on-chips in biomedical application

Drug screening is traditionally based on the pharmacodynamic models from 2D cell culture or animal experiments. However, these models suffer from poor drug efficacy prediction due to their difference from human in vivo cell microenvironments. In recent years, advances in biotechnology and tissue engineering have enabled rapid growth of in vitro organoid culturing. These organoids cultured in matrigel can mimic human in vivo cell microenvironment and physiology more accurately than traditional 2D cell culture and animal models. Among them, tumor organoids, especially patient-derived tumour organoids, can be applied as effective cancer models for drug screening and personalized medicine. By integrating organoid culturing and microfluidics, organoid-on-a-chip platform has been developed to simulate the structure and function of human tissues or organs. In 2010, Ingber et al. reported a biomimetic microfluidic platform called lung-on-a-chip. Microscale engineering technologies were firstly utilized to create biomimetic microchips. Henceforth, increasing kinds of organ-on-a-chips were reported all over the world to mimic different organs, such as liver, kidney and brain. 2D planar cells were cultured in PDMS chambers in majority organ-on-a-chips. More and more studies focused on 3D cells or organoids instead recently due to their better biomimetic capability for drug screening and disease models. In 2018, Qin et al. reported a liver organoid from human iPSCs in a 3D perfusable chip system, which is the first study that uses human organoid in a microfluidic chip and executed drug testing successfully. The established liver organoid-on-a-chip system may provide a promising platform for engineering stem cell-based organoids with applications in regenerative medicine, disease modeling and drug testing. Conventionally, drug efficacy evaluation in organoid-on-a-chip was performed by cell staining. However, this approach only presents static results of live/dead cells, but cannot monitor the cells dynamically for long-term recording. Sensor integration with organoid-on-a-chips paves a new way for dynamic recording. Currently, Wang et al. developed a 3D electric cell/matrigel-substrate impedance sensing (3D-ECMIS) platform for real-time and non-invasive monitoring of 3D cell viability and drug susceptibility. This platform integrated impedance sensors to monitor the impedance changes during 3D cell culturing. Additionally, Wang et al. reported the 3D cardiomyocytes detection by combining microelectrode arrays (MEAs). Heart cells of neonatal rat were cultured on a tissue engineering scaffold, which was fabricated by 3D printing and electro-spinning. The experimental results demonstrated that extracellular field potential (spike amplitude and firing rate) of 3D cardiomyocytes can be recorded in real time. Moreover, non-invasive measurement of cellular metabolism is important to study the metabolism mechanism and drug efficacy. Thus, light-addressable potentiometric sensor (LAPS) was integrated with organoid-on-a-chip for chemical imaging of ions (H+, Na+, K+, Ca2+) induced by cellular metabolism, which enables accurate detection of different chemical parameters in organoid-on-a-chip. Multiple organoid chip linked by microfluidics, called human-on-a-chip is a newly emerging and frontier technology to mimic the interaction of multiple human organs in recent years. It can recapitulate the physiologically relevant structures and functions of the organs, as well as the interaction between multiple organs as in vivo , thereby offering alternative models for predicting human responses to various drugs and environmental stimulus. Organoid-on-a-chip demonstrates outstanding potential in drug screening, disease modeling and personalized precision medicine.

Porous Graphene Oxide Enhanced Aptamer Specific Circulating-Tumor-Cell Sensing Interface on Light Addressable Potentiometric Sensor: Clinical Application and Simulation.

The circulating-tumor-cell (CTC) specific aptamer is believed to be a power recognition factor to realize clinical CTC assay. However, the limited sensing range is still one of the challenges in its real application. The porous-graphene-oxide (PGO) enhanced aptamer specific CTC sensing interface is studied on the platform of light-addressable-potentiometric-sensor (LAPS) to provide a clinical available method for CTC detection. The underlying mechanism of this sensing interface on LAPS is modeled and simulated. It is confirmed to be a promising candidate for CTC assay by the linear responding for 5-5000 spiked cells, as well as the satisfactory sensitivity for clinical samples.

Fluorographene sensing membrane in a light-addressable potentiometric sensor

A fluorographene sensing membrane on silicon nitride (Si3N4) for light-addressable potentiometric sensors (LAPS) is investigated. Three layers of monolayer graphene grown using low-pressure chemical vapor deposition (LPCVD) were transferred and stacked on a Si3N4 LAPS and then treated with CF4 plasma with a filter shielding. Clear fluorination of the 3-layer graphene is proven by studying the Raman spectrum, X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The pH sensitivity and linearity of this fluorographene sensing membrane are 56.8 mV/pH and 99.4%, respectively. The drift coefficient and hysteresis are 2.6 mV/h and 2.9 mV, respectively. This sensing performance is comparable to a Si3N4 sensing membrane. A significant negative bias shift in the photocurrent versus gate bias characteristics can be observed in the fluorographene sensing membrane, which could be explained by the fact that the work function increases owing to the dipole effect of carbon–fluorine bonds. A two-dimensional (2D) image of photocurrent measured in a pH 7 buffer solution for a sample with fluorographene and a Si3N4 sensing membrane on the same surface is generated by the scanning controlled by an XY stage and LAPS measurement system. The high and the low photocurrents of the fluorographene and Si3N4 sensing membrane can be clearly distinguished in the static 2D pH image with an appropriate gate bias voltage. Through these experimental results, fluorographene is proven to be a suitable pH-sensing membrane. Further study on surface immobilization is suggested for biomedical targets in the future.

Multi‐Well Sensor Platform Based on a Partially Etched Structure of a Light‐Addressable Potentiometric Sensor

A multi‐well‐structured light‐addressable potentiometric sensor (LAPS) plate is developed for measuring a plurality of sample solutions on a single sensor plate. It is also capable of high‐resolution chemical imaging inside the well structure. It can be applied, for example, to quantification of metabolic activities and imaging of biological samples incubated in the well structure. A minimum pattern size of 20 µm line is visualized and a wider frequency bandwidth of up to 200 kHz for the sensor signal is obtained in the well structure, which will be suitable for recording chemical images at a high‐frame‐rate.

DNA-Hybridization Detection on Si(100) Surfaces Using Light-Activated Electrochemistry: A Comparative Study between Bovine Serum Albumin and Hexaethylene Glycol as Antifouling Layers.

Light can be used to spatially resolve electrochemical measurements on a semiconductor electrode. This phenomenon has been explored to detect DNA hybridization with light-addressable potentiometric sensors and, more recently, with light-addressable amperometric sensors based on organic-monolayer-protected Si(100). Here, a contribution to the field is presented by comparing sensing performances when bovine serum albumin (BSA) and hexaethylene glycol (OEG6) are employed as antifouling layers that resist nonspecific adsorption to the DNA-modified interface on Si(100) devices. What is observed is that both sensors based on BSA or OEG6 initially allow electrochemical distinction among complementary, noncomplementary, and mismatched DNA targets. However, only surfaces based on OEG6 can sustain electroactivity over time. Our results suggest that this relates to accelerated SiO x formation occasioned by BSA proteins adsorbing on monolayer-protected Si(100) surfaces. Therefore, DNA biosensors were analytically explored on low-doped Si(100) electrodes modified on the molecular level with OEG6 as an antifouling layer. First, light-activated electrochemical responses were recorded over a range of complementary DNA target concentrations. A linear semilog relation was obtained from 1.0 × 10-11 to 1.0 × 10-6 mol L-1 with a correlation coefficient of 0.942. Then, measurements with three independent surfaces indicated a relative standard deviation of 4.5%. Finally, selectivity tests were successfully performed in complex samples consisting of a cocktail mixture of four different DNA sequences. Together, these results indicate that reliable and stable light-activated amperometric DNA sensors can be achieved on Si(100) by employing OEG6 as an antifouling layer.

Light-Addressable Potentiometric Sensors Using ZnO Nanorods as the Sensor Substrate for Bioanalytical Applications.

Light-addressable potentiometric sensors (LAPS) are of great interest in bioimaging applications such as the monitoring of concentrations in microfluidic channels or the investigation of metabolic and signaling events in living cells. By measuring the photocurrents at electrolyte-insulator-semiconductor (EIS) and electrolyte-semiconductor structures, LAPS can produce spatiotemporal images of chemical or biological analytes, electrical potentials and impedance. However, its commercial applications are often restricted by their limited AC photocurrents and resolution of LAPS images. Herein, for the first time, the use of 1D semiconducting oxides in the form of ZnO nanorods for LAPS imaging is explored to solve this issue. A significantly increased AC photocurrent with enhanced image resolution has been achieved based on ZnO nanorods, with a photocurrent of 45.7 ± 0.1 nA at a light intensity of 0.05 mW, a lateral resolution as low as 3.0 μm as demonstrated by images of a PMMA dot on ZnO nanorods and a pH sensitivity of 53 mV/pH. The suitability of the device for bioanalysis and bioimaging was demonstrated by monitoring the degradation of a thin poly(ester amide) film with the enzyme α-chymotrypsin using LAPS. This simple and robust route to fabricate LAPS substrates with excellent performance would provide tremendous opportunities for bioimaging.

Rapid determination of cadmium in rice using an all-solid RGO-enhanced light addressable potentiometric sensor

Herein, an all-solid light addressable potentiometric sensor (LAPS) is presented for determination of cadmium (Cd) in rice. On the working surface of the LAPS, reduced graphene oxide (RGO) is introduced as a part of ion-to-electron transducer to improve ionophore behaviors. The composite modification of RGO and ionophore is validated with scanning electron microscopy. The as-fabricated sensor presents a rapid response in less than 10 s to target Cd. Meanwhile, it shows lower noise (0.23 mV) and better limit of detection (0.002 mg L−1) than LAPS (control) without RGO modification (0.37 mV; 0.008 mg L−1). With the proposed method, satisfactory precision, accuracy and selectivity are also established. This method is adopted in an extensive survey for 25 rice samples from 5 regions in China. The results are in very good agreement with those obtained using inductively-coupled plasma-mass spectrometry.

A Partially Etched Structure of Light‐Addressable Potentiometric Sensor for High‐Spatial‐Resolution and High‐Speed Chemical Imaging

In this study, a partially etched structure of a light‐addressable potentiometric sensor (LAPS) is fabricated for high‐spatial‐resolution and high‐speed imaging of chemical species. An anisotropic etching process based on tetramethylammonium hydroxide (TMAH) is optimized to fabricate the structure, which strikes a balance between the imaging performance and the mechanical strength of the sensor plate. The etched region of the sensor plate with a thickness of 47 µm yields a 12‐fold enhancement of the photocurrent signal at a high frequency of 120 kHz and a 10‐fold frequency bandwidth in comparison with the frame region with a thickness of 150 µm due to the reduced traveling distance of charge carriers inside the semiconductor. This result represents a new approach for high signal‐to‐noise ratio, high‐spatial‐resolution, and high‐speed measurement.

Dual functional extracellular recording using a light-addressable potentiometric sensor for bitter signal transduction

This paper presents a dual functional extracellular recording biosensor based on a light-addressable potentiometric sensor (LAPS). The design and fabrication of this biosensor make it possible to record both extracellular membrane potential changes and ATP release from a single taste bud cell for the first time. For detecting ATP release, LAPS chip was functionalized with ATP-sensitive DNA aptamer by covalent immobilization. Taste bud cells isolated from rat were cultured on LAPS surface. When the desired single taste bud cell was illuminated by modulated light, ATP release from single taste bud cells can be measured by recording the shifts of bias voltage-photocurrent curves (I-V curves) when the LAPS chip is working in discrete mode. On the other hand, extracellular membrane potential changes can be monitored by recording the fluctuation of LAPS photocurrent when the LAPS chip is working in continuous mode. The results show this biosensor can effectively record the enhancive effect of the bitter substance and inhibitory effect of the carbenoxolone (CBX) on the extracellular membrane potential changes and ATP release of single taste bud cells. In addition, the inhibitory effect of CBX also confirms LAPS extracellular recordings are originated from bitter signal transduction. It is proved this biosensor is suitable for extracellular recording of ATP release and membrane potential changes of single taste bud cells. It is suggested this biosensor could be applied to investigating taste signal transduction at the single-cell level as well as applied to other types of cells which have similar functions to taste bud cells.