Light-addressable Potentiometric Sensor Research Articles

Actively Driven Light-Addressable Sensor/Actuator System for Automated pH Control for the Integration in Lab-On-A-Chip (LoC) Platforms.

The miniaturization of microfluidic systems usually comes at the cost of more difficult integration of sensors and actuators inside the channel. As an alternative, this work demonstrates the embedding of semiconductor-based sensor and actuator technologies that can be spatially and temporally controlled from outside the channel using light. The first element is a light-addressable potentiometric sensor, consisting of an Al/Si/SiO2/Si3N4 structure, that can measure pH changes at the Si3N4/electrolyte interface. The pH value is a crucial factor in biological and chemical systems, and besides measuring, it is often important to bring the system out of equilibrium or to adjust and control precisely the surrounding medium. This can be done photoelectrocatalytically by utilizing light-addressable electrodes. These consist of a glass/SnO2:F/TiO2 structure, whereby direct charge transfer between the TiO2 and the electrolyte leads to a pH change upon irradiation. To complement the advantages of both, we integrated a light-addressable sensor with a pH sensitivity of 41.5 mV·pH-1 and a light-addressable electrode into a microfluidic setup. Here, we demonstrated a simultaneous operation with the ability to generate and record pH gradients inside a channel under static and dynamic flow conditions. The results show that dependent on the light-addressable electrode (LAE)-illumination conditions, pH changes up to ΔpH of 2.75 and of 3.52 under static and dynamic conditions, respectively, were spatially monitored by the light-addressable potentiometric sensor. After flushing with fresh buffer solution, the pH returned to its initial value. Depending on the LAE illumination, pH gradients with a maximum pH change of ΔpH of 1.42 were tailored perpendicular to the flow direction. In a final experiment, synchronous LAE illumination led to a stepwise increase in the pH inside the channel.

A Silicon-Based Field-Effect Biosensor for Drug-Induced Cardiac Extracellular Calcium Ion Change Detection.

Calcium ions participate in the regulation of almost all biological functions of the body, especially in cardiac excitation-contraction coupling, acting as vital signaling through ion channels. Various cardiovascular drugs exert their effects via affecting the ion channels on the cell membrane. The current strategies for calcium ion monitoring are mainly based on fluorescent probes, which are commonly used for intracellular calcium ion detection (calcium imaging) and cannot achieve long-term monitoring. In this work, an all-solid-state silicone-rubber ion-sensitive membrane was fabricated on light-addressable potentiometric sensors to establish a program-controlled field-effect-based ion-sensitive light-addressable potentiometric sensor (LAPS) platform for extracellular calcium ion detection. L-type calcium channels blocker verapamil and calcium channel agonist BayK8644 were chosen to explore the effect of ion channel drugs on extracellular calcium ion concentration in HL-1 cell lines. Simultaneously, microelectrode array (MEA) chips were employed to probe the HL-1 extracellular field potential (EFP) signals. The Ca2+ concentration and EFP parameters were studied to comprehensively evaluate the efficacy of cardiovascular drugs. This platform provides more dimensional information on cardiovascular drug efficacy that can be utilized for accurate drug screening.

Silicon-based field-effect glucose biosensor based on reduced graphene oxide-carboxymethyl chitosan-platinum nanocomposite material modified LAPS

In this study, a label-free glucose (Glu) biosensor was designed by modifying reduced graphene oxide-carboxymethyl chitosan-platinum nanoparticles (RGO-CMCS-Pt NPs) on a silicon-based light-addressable potentiometric sensor (LAPS) based on the field effect tube principle. Under the bias voltage, a modulated light source is directed onto the semiconductor layer of the sensor, generating a weak photocurrent. Simultaneously, Glu is catalyzed by glucose oxidase (GOD) to produce gluconic acid and H2O2. The H2O2 further decomposes to facilitate electron transfer, disrupting the potential balance on the biosensor surface and causing changes in the photocurrent-bias voltage (I-V) curve. The voltage offset demonstrated a linear relationship with the Glu concentration ranging from 0.01 mg/mL to 4.0 mg/mL. The linear equation was △V= 19.17331 C+ 75.46574 (R2 =0.98831) with a high sensitivity of 19.17 mV*mL/mg and a low detection limit (LOD) of 0.01 mg/mL (S/N = 3). Furthermore, the Glu biosensor exhibited good specificity, reproducibility, and stability, the biosensor also realized the detection of glucose in human serum samples with a relative standard deviation ranging from 0.63% to 3.47%, and the results were consistent with the hospital's biochemical indicators, which demonstrated the potential application of the prepared biosensor in the clinical detection of Glu.

Light Addressable Potentiometric Sensors for Biochemical Imaging on Microscale: A Review on Optimization of Imaging Speed and Spatial Resolution.

Light addressable potentiometric sensors (LAPS) are a competitive tool for unmarked biochemical imaging, especially imaging on microscale. It is essential to optimize the imaging speed and spatial resolution of LAPS since the imaging targets of LAPS, such as cell, microfluidic channel, etc., require LAPS to image at the micrometer level, and a fast enough imaging speed is a prerequisite for the dynamic process involved in biochemical imaging. In this study, we discuss the improvement of LAPS in terms of imaging speed and spatial resolution. The development of LAPS in imaging speed and spatial resolution is demonstrated by the latest applications of biochemistry monitoring and imaging on the microscale.

Carbon-based light addressable potential sensor based on nitrogen-doped graphene quantum dots for detection of low-density lipoprotein

Cardiovascular diseases have become the number one killer of human health. Early diagnosis and treatment of cardiovascular diseases can effectively improve the treatment effect and reduce the disease death rate. As an important marker of cardiovascular disease, Low-Density Lipoprotein (LDL) can be used for the early detection of cardiovascular disease. In this study, a novel carbon-based Light Addressable Potentiometric Sensor (C-LAPS) for determination LDL has been constructed based on o-phenylenediamine modified nitrogen-doped graphene quantum dots/reduce graphene oxide (OPD@NGQDs/rGO) photosensitive layer. The OPD@NGQDs/rGO photosensitive layer has excellent photoelectric conversion efficiency, large specific surface area and good biocompatibility to enhance the response signal. For the determination LDL by the C-LAPS system, LDL binding to LDL aptamer causes a change in the surface potential of the photosensitive layer, producing a response signal that can be detected by the I-V curve. Under optimal conditions, the C-LAPS had a good linear relationship with LDL concentration in the range of 0.01 μg/mL- 0.15 μg/mL. The sensitivity was 1819 mV/µg·mL−1 and the limit of detection (LOD) was 6.43 ng/mL (S/N = 3). In addition, the C-LAPS showed good specificity, reproducibility, stability and satisfactory relative error for detecting LDL in human serum samples. Therefore, the C-LAPS has good performance and demonstrates potential clinical value.

Self-assembly crack metallic network applied on light-addressable potentiometric sensor for optimizing photoelectric conversion efficiency

Light-addressable potentiometric sensor (LAPS) is a kind of biochemical sensor based on semiconductor field effect addressed by light. In order to improve spatial resolution of chemical imaging system based on LAPS, metallic network is applied to suppress crosstalk. In this study, crack metallic network (CMN) is proposed to shrink electrode coverage and optimize photoelectric conversion efficiency. The crack pattern on colloidal film is used as template and crack metallic network is prepared on substrate surface by magnetron sputtering. LAPS with crack metallic network has a satisfactory sensor performance and a certain improvement of spatial resolution. Meanwhile, the coverage of crack metallic network remarkably reduces to 8.9 % and relative optical transmittance significantly increases to 90.95 %, corresponding to the photocurrent improvement. The results indicate crack metallic network effectively increases photocurrent magnitude under an acceptable spatial resolution.

A Summary of Recent Developments in Potentiometric Sensor Arrays

With upgrades in as far as possible and selectivity of ISEs, the presentation of new materials, new detecting ideas (from regular potentiometric to dynamic electrochemistry draws near), and more profound hypothetical getting it and displaying of the potentiometric reactions of ISEs, potentiometric in light of particle specific cathodes (ISEs) has encountered a renaissance. Ion sensors based on solid-state or polymeric membranes are currently available and can be used in sensor array formats for a variety of analytical applications. Coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs), and light-addressable potentiometric sensors (LAPS) are just a few of the strategies that have been developed to construct and use potentiometric sensor arrays based on various transduction principles. This review aims to provide a critical overview of these strategies. After reading recent papers on the development and applications of potentiometric sensor arrays, several issues and trends have been identified.

Rapid and specific detection of LDL based on light addressable potentiometric sensor decorated with reduced graphene oxide-polyaniline-hemin nanocomposites

Atherosclerotic Cardiovascular Disease (ASCVD) is one of the major fatal diseases for humans and the fatality rate is increasing rapidly. Low density lipoprotein (LDL) is a serum key marker in the diagnosis of ASCVD because LDL level is associated with the prevalence of ASCVD. Herein, a light addressable potentiometric sensor (LAPS) was constructed for rapid detection of LDL using reduced graphene oxide-polyaniline-hemin nanocomposites (RGO-PANI-HNCs) and low density lipoprotein aptamer (LDLapt) as sensitive membrane of LAPS. Under the effect of bias voltage, the specific binding between LDL and LDLapt, and forming the LDL-LDLapt complex will cause the voltage change on the sensitive membrane surface of the LAPS system, which will cause the change of original current–voltage (I-V) balance in the circuit, resulting in the shift of I-V curve. The correlation between the potential shift of LAPS and LDL concentration was linear from 1.0 to 100.0 μg/mL under optimal conditions. The sensitivity is 4.7671 mV/μg/mL, and the detection limit is 0.79 μg/mL. Also, the LDL biosensor showed satisfactory specificity, selectivity, reproducibility, and showed a good precision in real human serum samples, which provides a simple and effective way for the early diagnosis of ASCVD.

Trench Bottom Optical Isolation for Suppressing Lateral Diffusion of Photocarriers in LAPS

Lateral diffusion of photocarriers in substrate causes the cross-talk in light-addressable potentiometric sensor (LAPS), which degrades the performance of LAPS. Surface optical isolation is a useful method to suppress the cross-talk in LAPS of backside irradiation manner, but the remarkable reduction of detection signal is a defect. In this study, a method of trench bottom optical isolation is developed. Main idea of this method is using the trench structure to narrow the diffusion scope of photocarriers, then irradiating the trench bottom by isolation light to locally suppress cross-talk. According to experimental analysis, when using 400 μm thick substrate, 240 μm deep trench and 100 mA drive current of isolation laser, the suppressing ability of trench bottom optical isolation is 1.38 times as strong as surface optical isolation, and 3.14 times as strong as having no isolation. Besides, the detection signal intensity of trench bottom optical isolation is 1.4 times as great as surface optical isolation. Thus, the method of trench bottom optical isolation can effectively suppress the cross-talk and reduce the loss of detection signal.

Triple-helix molecular switch-based light-addressable potentiometric aptasensor for the multi-channel highly sensitive label-free detection and spatiotemporal imaging of okadaic acid

Okadaic acid (OA) has attracted considerable attention in the fields of human health and public safety because it can cause severe virulence and is widely distributed. Therefore, it is of immediate significance to explore a novel method for highly sensitive, low-consumption, efficient, and convenient OA detection. In this study, a triple-helix molecular switch (THMS)-based light-addressable potentiometric aptasensor (LAPA) is proposed for the highly sensitive and selective label-free detection and spatiotemporal imaging of OA. In this method, a THMS containing an OA aptamer served as the recognition element, and a DNA microarray including a light-addressable potentiometric sensor was designed as the transducer. Meanwhile, poly (allylamine hydrochloride) was modified on the chip surface to enhance DNA absorption and signal detection. A detection platform was constructed to measure signals and scan spatiotemporal images. The realized biosensing system enabled the multichannel detection of OA in a linear range of 0.05–100 nM with low sample consumption, a detection limit of 0.03 nM, and a detection time of 27 min/channel and spatiotemporal imaging analysis with a resolution of 400 µm2/pixel and frame duration of 3.2 min/frame. Considering the technical developing of aptamer-based THMS and micro/nano biosensor, the proposed method will provide a promising approach for label-free detection and spatiotemporal analysis of OA with high sensitivity, specificity, and detection efficiency; low sample dosage; and simple operation.

An organic semiconductor obtained with a low-temperature process for light-addressable potentiometric sensors

In this study, the first trial of donor and acceptor bulk heterojunctions (BHJs) is proposed for light-addressable potentiometric sensors (LAPSs) due to organic conjugated molecules with the advantages of energy level/band gap modification and high absorption of visible light. The benzodithiophene-based polymer PTB7-Th and fullerene PC71BM are selected for integration with an Al2O3 sensing membrane using atomic layer deposition at temperatures lower than 100 ℃ for pH sensing LAPS. In the stability performance, the hysteresis width of the best condition with a mixing weight ratio of PC71BM to PTB7-Th of 1.5 is 4.4 mV, which is inferior to that of the conventional inorganic semiconductor-based LAPSs. By means of an additional spin-coated zinc oxide (ZnO) layer, the signal-to-noise ratio of the photocurrent of this fabricated LAPS can be maintained at 3.2 after 170 min of measurement with an acceptable sensitivity, linearity, drift coefficient and hysteresis of 50.2 mV/pH, 99.9%, − 3.1 mV/h and 1.4 mV, respectively. With the proper adjustment of illumination with low power and large spots, chemical imaging with a scanning step of 25 µm can be conducted to indicate the feasibility of this low-temperature process developed for spin-coated organic semiconductor-based LAPSs.

Photoelectrochemical imaging of single cardiomyocytes and monitoring of their action potentials through contact force manipulation of organoids

Accurate monitoring of cardiomyocyte action potentials (APs) is essential to understand disease propagation and for trials of novel therapeutics. Patch clamp techniques offer ‘gold standard’ measurements in this field, but are notoriously difficult to operate and only provide measurements of a single cell. Here we propose photoelectrochemical imaging (PEI) with light-addressable potentiometric sensors (LAPS) in conjunction with a setup for controlling the contact force between the cardiomyocyte organoids and the sensor surface for measuring APs with high sensitivity. The method was validated through measuring the responses to drugs, and the results successfully visualized the expected electrophysiological changes to the APs. PEI allows for several cells to be monitored simultaneously, opening further research to the electrophysiological interactions of adjoining cells. This method expands the applications of PEI to three-dimensional geometries and provides the fields of stem cell research, drug trials and heart disease modelling with an invaluable tool to further investigate the role of APs.

A rGO-PAM-Fc/AuNPs nanosensing membrane in a light-addressable potentiometric biosensor for 1,5-anhydroglucitol determination

1,5-anhydroglucitol (1,5-AG) is an important indicator in the early detection of diabetes. In this study, a high-performance light addressable potentiometric sensor (LAPS) for the detection of 1,5-AG based on reduced graphene oxide-polyacrylamide-ferrocene/gold nanoparticles (rGO-PAM-Fc/AuNPs) as sensing membrane and pyranose oxidase (PROD) as the specific recognition substance was constructed. Among them, rGO-PAM-Fc/AuNPs modification LAPS chip can not only effectively increase the specific surface area and adsorb more PROD, but also enhance the capacitive effect of LAPS and improve the detection sensitivity. 1,5-AG is hydrolyzed by PROD and produces hydrogen peroxide (H2O2) that can oxidize divalent ferrocene ions in the rGO-PAM-Fc composite to trivalent ferrocene ions, therefore leads to a change in the membrane potential on the surface of the LAPS chip and causes a shift in the I-V curve, which reflect the change of 1,5-AG concentration. The designed LAPS had a good linearity with 1,5-AG concentration in the range of 100.0–1000.0 μg/mL with a correlation coefficient of 0.99068. The sensitivity was calculated to be 0.1908 mV/μg/mL and a limit of detection (LOD) of 21.74 μg/mL was obtained using three signal-to-noise ratio (S/N = 3). Also, the 1,5-AG biosensor has good specificity, reproducibility and stability, and can be used in human serum samples with the recoveries of 93.62 %–114.52 %. This work provides a highly sensitive, portable and low-cost assay for the detection of 1,5-AG. Prime novelty statementHerein, a high-performance light addressable potentiometric sensor (LAPS) for the detection of 1,5-AG based on reduced graphene oxide-polyacrylamide-ferrocene/gold nanoparticles (rGO-PAM-Fc/AuNPs) as sensing membrane and pyranose oxidase (PROD) as the specific recognition substance was constructed. Among them, rGO-PAM-Fc/AuNPs modification LAPS chip can not only effectively increase the specific surface area and adsorb more PROD, but also enhance the capacitive effect of LAPS and improve the detection sensitivity. 1,5-AG is hydrolyzed by PROD and produces hydrogen peroxide (H2O2) that can oxidize divalent ferrocene ions in the rGO-PAM-Fc composite to trivalent ferrocene ions, therefore leads to a change in the membrane potential on the surface of the LAPS chip and causes a shift in the I-V curve, which reflect the change of 1,5-AG concentration. The designed LAPS had a good linearity with 1,5-AG concentration in the range of 100.0–1000.0 μg/mL with a correlation coefficient of 0.99068. The sensitivity was calculated to be 0.1908 mV/μg/mL and a limit of detection (LOD) of 21.74 μg/mL was obtained using three signal-to-noise ratio (S/N = 3). Also, the 1,5-AG biosensor has good specificity, reproducibility and stability, and can be used in human serum samples with the recoveries of 93.62 %–114.52 %. This work provides a highly sensitive, portable and low-cost assay for the detection of 1,5-AG.

A differential light addressable potentiometric sensor using solid-state reference

The differential light addressable potentiometric sensor (LAPS) can provide low-background measurement for chemicals. For the conventional differential LAPS system, the acquisition of reference signal requires liquid participation. In this study, a differential LAPS with solid-state reference (SSR) is presented for pH measurement, where SSR based on the structure of metal-insulator-semiconductor is used as reusable reference signal source. In order to facilitate the differential signal matching and realize the effect of large reduction of background signal, an intelligent method to match the amplitude and phase between LAPS output and SSR output by controlling the illumination excitation of SSR is proposed. Effect of SSR as reference signal source for differential LAPS is studied, which is including pH sensing and chemical image performance. As an auxiliary liquid-free chip, SSR can assist the differential LAPS to realize low-background pH measurement conveniently and flexibly.

Light addressable potentiometric sensor with well-ordered pyramidal pits-patterned silicon

Light addressable potentiometric sensor (LAPS) with the structure of electrolyte-insulator-semiconductor is a kind of field effect sensor that detects local potential changes caused by protonation and deprotonation between electrolyte and insulator by light pulse. And scanned light pulse allows two-dimensional imaging of the distribution of chemical/biological species on the surface of sensor. An important challenge is to achieve low-cost, strong anti-interference and high-performance silicon-based LAPS. In this study, we propose to combine microsphere lithography with wet etching to fabricate well-ordered, tunable and low-cost pyramidal pits-patterned silicon as semiconductor of LAPS. The morphology and optical properties of pyramidal pits-patterned silicon are tested and analyzed. The sensing characteristics and the pH imaging performance of LAPS are tested and evaluated. The experiment results and theoretical analyses show that LAPS with pyramidal pits-patterned silicon has acceptable pH response, good long-term stability, and high performance in terms of photocurrent enhancement ratio, signal-to-noise ratio and pH imaging. This work can provide a simple, low-cost, strong anti-interference and high-performance device for pH-related chemical/biological analysis.

Urease-modified LAPS: Two-dimensional dynamic detection of enzymatic reactions

• Urea-sensitive LAPS fabricated by a layer-by-layer self-assembly technique. • The enzymatic reactions are monitored dynamically in spatially resolved manner. • A method for the selection of monitoring windows based on threshold intersections. • The 2D images are more uniform and reduce demand for the number of pixel points. Light addressable potentiometric sensor (LAPS) is a semiconductor-based electrochemical sensor with flat surface structure and superior light addressability, making it an ideal platform for visualizing enzymatic reactions. However, it is hardly to observe the true process of reactions because a large amount of information unrelated to the enzymatic reaction, such as buffer diffusion caused by pH gradient, is contained in photocurrent images. In this study, urea-sensitive LAPS were obtained by immobilizing urease on the surface of LAPS with Si/SiO 2 /Si 3 N 4 structured using a layer-by-layer self-assembly technique and a method for the selection of enzymatic reaction monitoring windows based on threshold intersections is proposed to reduce the influence of non-enzymatic reaction factors. The overall performance of the urea-sensitive LAPS was excellent, with a sensitivity of 92.04 ± 4.04 mV/pC urea and a linearity of 99.16 % in the range of 1–20 mM. The mean square error of photocurrent images using this method is reduced by an order of magnitude compared to original images, which are more uniform and reduce the pixel demand. Our work provides a more complete assessment of urea-sensitive LAPS, and the proposed window selection method based on threshold intersections provides a viable method for dynamic monitoring of chemical images with high uniformity and high refresh rates.

Visualization of electrochemical reactions on microelectrodes using light-addressable potentiometric sensor imaging

Visualization of the electrochemical reaction is essential for comprehensively understanding the electrochemical reaction mechanism and precisely characterizing dynamic electrochemical processes. Herein, we propose a simple device that combines light-addressable potentiometric sensor (LAPS) imaging and microelectrodes to serve as a general electroanalysis platform for the label-free sensing and imaging of electrochemical reactions. In this device, two microelectrodes are assembled on the LAPS chip. Electrochemical reactions occurring on the microelectrodes can be qualitatively and quantitatively observed and visualized using a LAPS chip that is sensitive to the reaction products. Validations were performed to monitor the effect of water electrolysis and potassium ferrocyanide oxidation surrounding the microelectrodes, respectively. We believe that this study will provide an excellent platform for the visualization and monitoring of electrochemical reactions and broaden the application scope of LAPS imaging to a general electroanalysis tool that is widely applicable in several fields.

Label-free detection of glypican-3 using reduced graphene oxide /polyetherimide/gold nanoparticles enhanced aptamer specific sensing interface on light-addressable potentiometric sensor

Glypican-3 (GPC3) protein is considered as an effective and specific biomarker for the accurate diagnosis of hepatocellular carcinoma (HCC), and there is a critical demand to construct strategies with shorter time, lower cost noise and higher sensitivity. In this study, a biosensor for label-free detection of GPC3 was prepared by modifying GPC3 aptamer (GPC3Apt) on the surface of Si-based light addressable potentiometric sensor (LAPS) chip modified by reduced graphene oxide/polyetherimide/gold nanoparticles (rGO/PEI/AuNPs). Among them, GPC3Apt with a low equilibrium dissociation constant was used as a biorecognition molecule to recognize and capture GPC3. The rGO/PEI/AuNPs decorated on the LAPS surface could enlarge the surface area for GPC3Apt immobilization and provide more active sites for GPC3Apt to bind effectively with the target GPC3. When a bias voltage was provided to the LAPS system, the forming GPC3-GPC3Apt complexs on the sensing interface of LAPS would cause the potential of the sensitive membrane surface to change and generate a corresponding offset response in photocurrent-voltage (I-V) curves. The potential shift and GPC3 concentration showed a good linear range from 0.1 to 100.0 μg/mL with a detection limit of 40.0 ng/mL (S/N = 3) and a sensitivity of 1.33638 mV/μg/mL. In addition, the LAPS detection system also has good specificity and stability, which can be used for the detection of GPC3 in spiked serum samples.

Light-Addressable Electrochemical Sensors toward Spatially Resolved Biosensing and Imaging Applications

The light-addressable electrochemical sensor (LAES) is a recently emerged bioanalysis technique combining electrochemistry with the photoelectric effect in a semiconductor. In an LAES, a semiconductor substrate is illuminated locally to generate charge carriers in a well-defined area, thereby confining the electrochemical process to a target site. Benefiting from the unique light addressability, an LAES can not only detect multiple analytes in parallel within a single sensor plate but also act as a bio(chemical) imaging sensor to visualize the two-dimensional distribution of specific analytes. An LAES usually has three working modes: a potentiometric mode using light-addressable potentiometric sensors (LAPS) and an impedance mode using scanning photoinduced impedance microscopy (SPIM), while an amperometric mode refers to light-addressable electrochemistry (LAE) and photoelectrochemical (PEC) sensing. In this review, we describe the detection principles of each mode of LAESs and the concept of light addressability. In addition, we highlight the recent progress and advance of LAESs in spatial resolution, sensor system design, multiplexed detection, and bio(chemical) imaging applications. An outlook on current research challenges and future prospects is also presented.

Efficient Illumination for a Light-Addressable Potentiometric Sensor.

A light-addressable potentiometric sensor (LAPS) is a chemical sensor that is based on the field effect in an electrolyte–insulator–semiconductor structure. It requires modulated illumination for generating an AC photocurrent signal that responds to the activity of target ions on the sensor surface. Although high-power illumination generates a large signal, which is advantageous in terms of the signal-to-noise ratio, excess light power can also be harmful to the sample and the measurement. In this study, we tested different waveforms of modulated illuminations to find an efficient illumination for a LAPS that can enlarge the signal as much as possible for the same input light power. The results showed that a square wave with a low duty ratio was more efficient than a sine wave by a factor of about two.