Optoelectrochemical Sensor Research Articles

Enhanced detection of glyphosate with a Co-MOF integrated opto-electrochemical sensor

Abstract This study presents a new method for detecting the organophosphorus pesticide glyphosate using advanced scanning electrodes (SPE) and enhanced fluorescence. Metal-organic frameworks from cobalt ions were synthesized using a solvothermal method. It is characterized using Raman spectroscopy, FT-IR, and X-ray diffraction techniques. The electrocatalytic behavior of the materials was studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) examined the positive response of plants to glyphosate over a concentration range of 0.55–5.95 mM with a detection limit of 0.334 mM. The fluorescence enhancement ranges from 0.07 mM to 0.67 mM, and the detection limit is 0.0998 mM. Additionally, the selectivity of the proposed opto-electrochemical sensor was evaluated. This selection demonstrates the sensor's ability to detect glyphosate in complex wastewater matrices. This has important implications for environmental monitoring. By addressing glyphosate contamination, the sensor could significantly advance ecological remediation and monitoring strategies. The selectivity, sensitivity, and ability to operate under harsh conditions represent a significant advance in the development of efficient and reliable glyphosate technology for wastewater treatment and environmental protection. In real-sample matrices, the suggested sensor showed a good recovery of the pesticide that had been spiked.

Smartphone enabled machine learning approach assisted copper (II) quantification and opto-electrochemical explosive recognition by Aldazine-functionalized chemobiosensor

An Aldazine-based optoelectrochemical sensor, BMH (1-(quinolin-4-ylmethylene)hydrazono)methyl)naphthalen-2-ol) has been introduced herein for selective detection of aqueous copper (Cu2+) and 2, 4, 6-Trinitrophenol (TNP) at an ultra-low level detection limit (0.09 ppm for Cu2+ and 0.019 ppm for TNP). Multichannel recognition aptitude of the chemosensor (BMH) towards both Cu2+ and TNP along with bountiful practical applications ascertained it as an innovative one in the environmental and biomedical domains. BMH can detect Cu2+ in water, fetal bovine serum, and human urine samples, while explosive TNP can be identified in water, soil, and matches powder. The intracellular Cu2+ and TNP recognition efficiencies of BMH have been investigated in human lung cancer cell lines (A459). The hassle-free smartphone ensemble machine learning approach for Cu2+quantification has been introduced which would certainly be a significant addition in the domain of water quality analysis. Moreover, the ethylenediaminetetraacetic acid (EDTA) mediated reversibility of the probe could serve as a logic gate imitating electrical circuitry.

Copper-pyridine-2,4,6-tricarboxylate metal organic framework nanoparticles based opto-electrochemical sensor for sensitive detection of matrix metalloproteinase‑2

We designed a multiple signal sensing probe based on highly luminescent nanosized Cu-PTC metal-organic framework (MOF). The as synthesized nano-MOF was characterized by various techniques to confirm its morphology, crystallinity and elemental composition. A positively charged matrix metalloproteinase-2 (MMP-2) substrate (a polypeptide) was designed and prepared to interact electrostatically with the negatively charged Cu-PTC MOF probe, resulting in decrease in fluorescence response of the probe. Subsequently, MMP-2 was specifically recognized by the MMP-2 substrate and cleavage of the MMP-2 substrate resulted in “turn-on” fluorescence response from 1 to 175 ng/mL of MMP-2 concentrations with a limit of detection (LOD) of 0.8 ng/mL. In addition, the developed Cu-PTC MOF also exhibited peroxidase-like activity, which was exploited in the electrochemical detection of MMP-2 subjected to the catalysis of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2. The large surface area of the probe and unique catalytic activity toward TMB facilitated fabrication of an excellent sensing platform to detect MMP-2 with a linear range of 0.5–200 ng/mL with a LOD of 0.25 ng/mL. Various potential interfering biomolecules were evaluated and the stability of the constructed biosensor was assessed in optical and electrochemical modes. The reliability of the electrochemical detection mode was further executed by monitoring MMP-2 in biological samples (human serum and cell samples) and good recoveries were recorded.

Metal-organic framework-based nanomaterials as opto-electrochemical sensors for the detection of antibiotics and hormones: A review.

Increasing trace levels of antibiotics and hormones in the environment and food samples are concerning and pose a threat. Opto-electrochemical sensors have received attention due to their low cost, portability, sensitivity, analytical performance, and ease of deployment in the field as compared to conventional expensive technologies that are time-consuming and require experienced professionals. Metal-organic frameworks (MOFs) with variable porosity, active functional sites, and fluorescence capacity are attractive materials for developing opto-electrochemical sensors. Herein, the insights into the capabilities of electrochemical and luminescent MOF sensors for detection and monitoring of antibiotics and hormones from various samples are critically reviewed. The detailed sensing mechanisms and detection limits of MOF sensors are addressed. The challenges, recent advances, and future directions for the development of stable, high-performance MOFs as commercially viable next-generation opto-electrochemical sensor materials for the detection and monitoring of diverse analytes are discussed.

Zirconium metal organic framework based opto-electrochemical sensor for nitrofurazone detection

The manuscript presents a zirconium metal–organic framework (Zr-MOF or UiO-66-NH2) based efficient sensing system to detect nitrofurazone (NFZ) antibiotic, by employing electrochemical-optical dual detection technique. The Zr-MOF was synthesized by solvothermal method and the success of synthesis was confirmed by using analytical techniques of characterization. For electrochemical determination of NFZ, electrodeposited gold nanoparticles supported zirconium metal–organic framework modified screen-printed electrode (AuNPs/UiO-66-NH2/SPCE) was used. As prepared electrochemical sensing platform showed a wide linear concentration range of 1x10−8 to 5x10−5 mol/L for NFZ. For fluorometric measurements, synthesized UiO-66-NH2 was employed under optimized conditions, and a turn-off behavior of NFZ towards UiO-66-NH2 was observed from a range of concentration 1x10−8 to 4.5x10−5 mol/L of NFZ. The proposed opto-electrochemical sensor attained low detection limit in nM range, showed selective behavior in presence of other antibiotics, and gave a reproducible signal with the RSD value less than 2.5% (n = 5). The prepared sensor was tested to detect NFZ in lake water samples and the results indicated good percentage recovery in the range 97.70–98.40 and 93.30–97.84%, for electrochemical and optical methods, respectively.

Hybrid Optoelectrochemical Sensor for Superselective Detection of 2,4,6-Trinitrotoluene Based on Electrochemical Reduced Meisenheimer Complex

2,4,6-Trinitrotoluene (TNT) is known as one of the most used explosives, and its detection is significant in public security, human health, and environmental protection. The fabrication of absorbance based optical sensors for TNT is a serious challenge due to poor selectivity and sensitivity. We reported the design and fabrication of a superselective hybrid optoelectrochemical sensor based on the electrochemical reduction of Meisenheimer complex in a deep eutectic solvent (DES) modified with n-butylamine (nBA) for determination of TNT. The hybrid optoelectrochemical sensor (HOPES) that placed in DES modified with nBA and also an optical sensor (OPS) were fabricated. The electrochemical reduction of Meisenheimer complex occurred at HOPES when the potential was applied and consequently the sensing performance (sensitivity and selectivity) was dramatically enhanced compared to OPS. The both OPS and HOPES responded linearly to TNT with detection limits of 310 and 8 nmol L-1, respectively. The selectivity observed for the HOPES toward TNT compared to the other interferences was enhanced by a factor of 103-104, thus we can use the term "superselectivity" for HOPES. The mechanism of HOPES response was proved by optoelectrochemical and electrochemical impedance spectroscopy (EIS) techniques. The field emission scanning electron microscope (FESEM) was employed for the characterization of electrodeposited Meisenheimer layer. Finally, we presented a proposed model for the sensing mechanism of OPS and HOPES based on TNT complexation in the absence and presence of electric potential, respectively.

Novel nanostructured indium tin oxide electrode for electrochemical immunosensors: Suitability for the detection of TNF-α

The need for new and innovative point of care (POC) systems providing a feasible alternative to costly and time consuming standard laboratory techniques is becoming more evident every day, particularly in the case of cardiovascular diseases. Coupling optical and electrochemical principles for highly specific and sensitive detection of biomarkers could boost the successful implementation of POC systems in biomedical environments. We suggest indium tin oxide (ITO) as a promising material for working electrodes in optoelectrochemical sensors, owing to the rare combination of high electrical conductivity and optical transparency it presents. Moreover, the nanostructured nature of the electrodes' surface is crucial for an eventual miniaturization of the POC system. In this work, we describe the construction and characterization of a nanostructured ITO electrode modified with aryl diazonium salt as transparent substrate for electrochemical immunosensors. The developed electrode was tested for the detection of tumour necrosis factor α (TNF-α), a cardiac biomarker playing an important role in the prevention of heart failure. Macro and microscopic evidences (gathered from electrochemical and spectral techniques) of covalent bonding and high surface coverage are provided. Specific interaction between antigen (TNF-α) and monoclonal antibody (Ab-TNF-α) was verified by fluorescence patterning, confirming the proper bio-recognition of the cytokine. As a proof-of-concept, results of electrochemical impedance spectroscopy (EIS) show stabilized semi-quantitative label-free detection of TNF-α at several concentrations (from 10 pg/mL to 100 pg/mL). These preliminary results demonstrate the feasibility of using transparent substrates for the detection of cytokines at low concentrations, and the consequent application in POC systems for the monitoring of cardiovascular diseases.

Transparent Nanowire Electrodes As a Tool for Electrochemical Detection

The development of new nanomaterial like carbon nanotubes, graphene and nanowires brings new possibilities to existing technologies. With the emergence of transparent electrode based on these materials, we could imagine new type of sensors, which combines transparency and flexibility. Silver nanowire transparent electrodes are currently transforming this industry. Touch screen sensors, OLED and solar panel can now be fabricated on flexible plastic sheets with low cost printing techniques. In the same way, this new type of electrode could bring electrochemical sensor toward new transparent and flexible sensing application for life science. In our study, we fabricate and characterize transparent electrode based in metal nanowires for electrochemical detection. By changing the length, diameter and amount of deposited nanowires, we can vary their transparency (up to 90% transparent), sheet resistance (up to 0.1 ohm/square) and effective surface area. Compared to conventional evaporated plain electrodes, printed nanowire electrodes can achieve more than 80% transparency (in visible range) with the same electrochemical effective surface area. Using these electrodes, we can fabricate new sensors with high transparency (> 90%), flexibility and high sensitivity to oxygen and hydrogen peroxide. The detection of these two components is predominant in healthcare and environmental monitoring. The combination of those properties could allow us to use this type of sensors as opto-electrochemical sensors for monitoring living cells and also for glucose detection on humans. Transparent nanowire electrodes can also be a real alternative to existing indium tin oxide (ITO) transparent electrodes for other applications. Figure 1.Pictures of electrochemical sensors based on metal nanowires on PET transparent substrate. WE and REF electrodes are made from metal nanowire have 80% transparency, CE electrode are made from gold. Figure 2. SEM image of silver nanowire electrode and the size distribution of nanowires. Figure 3. Voltammetry response of the nanowire based electrochemical sensor to hydrogen peroxide in phosphate buffer (pH=7) Figure 4. Dose-response curve to hydrogen peroxide using the nanowire-based sensor in phosphate buffer (pH=7) Figure 1

Optoelectrochemical Biorecognition by Optically Transparent Highly Conductive Graphene-Modified Fluorine-Doped Tin Oxide Substrates

Both optical and electrochemical graphene-based sensors have gone through rapid development, reaching high sensitivity at low cost and with fast response time. However, the complex validating biochemical operations, needed for their consistent use, currently limits their effective application. We propose an integration strategy for optoelectrochemical detection that overcomes previous limitations of these sensors used separately. We develop an optoelectrochemical sensor for aptamer-mediated protein detection based on few-layer graphene immobilization on selectively modified fluorine-doped tin oxide (FTO) substrates. Our results show that the electrochemical properties of graphene-modified FTO samples are suitable for complex biological detection due to the stability and inertness of the engineered electrodic interface. In addition, few-layer immobilization of graphene sheets through electrostatic linkage with an electrochemically grafted FTO surface allows obtaining an optically accessible and highly conductive platform. As a proof of concept, we used insulin as the target molecule to reveal in solution. Because of its transparency and low sampling volume (a few microliters), our sensing unit can be easily integrated in lab-on-a-chip cell culture systems for effectively monitoring subnanomolar concentrations of proteins relevant for biomedical applications.

Electrochemical signal response for vitamin B1 using terbium luminescent nanoscale building blocks as optical sensors

A luminescent terbium complex was covalently modified onto anisotropic gold nanostructures (nanoparticles and nanorods) respectively. Two novel emissive gold nanoprobes were successfully developed for selective and rapid determination of vitamin B1 in water. More significantly, electrochemical sensing performances were investigated based on green emissive gold nanoparticles and nanorods which were fabricated by anchoring gold nano-sensors on the surface of glassy carbon electrodes. Both the fluorescence spectra and cyclic voltammetry curves exhibited selective signal changes in the presence of vitamin B1 in comparison with vitamin B2, B3, B4, B5 and B6. It is considered to be the first example that different dimensional fluorescent nano-probes were selected and applied as dual opto-electrochemical sensors for recognizing the same analyte.

Towards Hyphenated Sensors Development: Design and Application of Porphyrin Electropolymer Materials

AbstractThe peculiar properties of porphyrins allow their exploitation as sensing materials in chemical sensors having different transduction principles, or even the intriguing possibility to develop sensors where two different transduction mechanisms are hyphenated in the same substrate. This approach can allow a significant increase in the chemical information obtained from the device and it can boost the performances in terms of selectivity and sensitivity. Our recent achievements in the field of functionalized porphyrins application for the development of the hyphenated optoelectrochemical sensors will be discussed in this contribution.

Electrochemiluminescent detection of hydrogen peroxide with an imaging sensor array

In this paper, we report a novel imaging sensor array for the electrochemiluminescent (ECL) detection of hydrogen peroxide. An ordered array of opto-electrochemical sensors was fabricated on the distal face of a coherent optical fiber bundle. The analytical performance and the ability to perform concomitantly ECL imaging and white-light imaging via the sensor array are described. Luminol ECL was generated at the distal face of the sub-micrometer sensor array by applying an adequate positive potential. The electrochemically-initiated light is transmitted through the coherent imaging sensor array and acquired on the proximal face with a microscope/charge coupled device (CCD) camera system. The influence of the potential applied to the sensor array on the light intensity collected via the array itself was investigated. The variation of the ECL intensity with hydrogen peroxide concentration is linear between 50 μM and 2 mM with a detection limit of 10 μM. The ECL sensor array also showed good temporal stability. Finally, the optical performance and the resolution of the sensor array were demonstrated in the micrometer range by imaging carbon fibers of 10 μm diameter.

Development of an ordered array of optoelectrochemical individually readable sensors with submicrometer dimensions: application to remote electrochemiluminescence imaging.

A novel array of optoelectrochemical submicrometer sensors for remote electrochemiluminescence (ECL) imaging is presented. This device was fabricated by chemical etching of a coherent optical fiber bundle to produce a nanotip array. The surface of the etched bundle was sputter-coated with a thin layer of indium tin oxide in order to create a transparent and electrically conductive surface that is insulated eventually by a new electrophoretic paint except for the apex of the tip. These fabrication steps produced an ordered array of optoelectrochemical sensors with submicrometer dimensions that retains the optical fiber bundle architecture. The electrochemical behavior of the sensor array was independently characterized by cyclic voltammetry and ECL experiments. The steady-state current indicates that the sensors are diffusively independent. This sensor array was further studied with a co-reactant ECL model system, such as Ru(bpy)(3)(2+)/TPrA. We clearly observed an ordered array of individual ECL micrometer spots, which corresponds to the sensor array structure. While the sensors of the array are not individually addressable electrochemically, we could establish that the sensors are optically independent and individually readable. Finally, we show that remote ECL imaging is performed quantitatively through the optoelectrochemical sensor array itself.

Opto-electrochemical planar wave-guide sensor for copper (II) ion

An opto-electrochemical sensor for copper (II) ion was developed. The sensor consists of a planar conductive indium–tin–oxide (ITO) glass support, which was coated by a polymeric copper (II) sensitive membrane. The sensing membrane is made of plasticized polyurethane matrix containing Zincon colorimetric reagent immobilized as ion pair with tetraoctylammonium ion. The instrumentation used commonly for wave-guide sensor development was extended with a potentiostat that made possible the control of the electric potential of the conductive surface. In this way the transport rate of ionic species through the membrane–sample interface could be influenced. In the presence of copper (II) ions the color of the membrane turned from red to blue, which was monitored optically. By applying positive potential to the conductive surface the direction of the ion diffusion at the membrane/sample interface was changed. As a result the sensing layer was regenerated within 2 minutes and was ready for further measurement. The sensor measured Cu 2+ ion in a concentration range of 1–200 μM.

Optoelectrochemical sensor for lead based on electrochemically assisted solvent extraction

A thin film containing the complexing agent 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP) deposited on the surface of an indium tin oxide (ITO) electrode has been used as a colorimetric sensor for lead. The sensor is based on a new electrochemically assisted solvent extraction method. When a cathodic potential was applied to the thin-film sensing layer, lead ions were extracted from the aqueous solution into the film resulting in an increase of absorbance at 550 nm. The magnitude of the absorbance change was linearly dependent on the concentration of lead in the range 0–5 ppm with an estimated limit of detection for a simple spectrophotometric method better than 250 ppb. The sensor was reset for a fresh measurement by applying an anodic potential. The prospects for using this electroassisted extraction method in conjunction with the optical waveguide evanescent field detection as a new integrated sensor for trace analysis are discussed. A sensitivity better than 10 ppb is predicted for this configuration.

Electrochemically-controlled waveguide-coupled surface plasmon sensing

A surface plasmon resonance sensing device has been constructed, in which excitation of a surface plasmon on a metal film is achieved by coupling from light propagating in an optical waveguide. The metal film cladding has been used as an electrode surface and it is proposed that these structures may be applied as novel optoelectrochemical sensors. Specific cationic adsorption has been monitored in potential regions where the metal free-electron contribution is small, and the sensitivity of this sensing technique has been deduced by comparison with ellipsometric measurements. The interfacial model used to analyse the ellipsometric results has been tested by calculating coverage by water in the water + ethylene glycol mixture employed in the surface plasmon device. The high sensitivity of this technique to adsorbed films is found to be greater than that predicted by the theoretical model described, and reasons for this discrepancy are discussed.

An optoelectrochemical thin-film chlorine sensor employing evanescent fields on planar optical waveguides

A new type of optoelectrochemical sensor based on an electrochromic thin-film sensing layer placed on top of a planar waveguide has been developed. The oxidation state of the sensing film is quantitatively measured by the evanescent field of the light transmitted through the waveguide. The functioning of the device has been ascertained which dissolved chlorine, employing an electrochemically resettable film of lutetium biphthalocyanine. Detection of film oxidation has been carried out at 950 nm. This technique appears promising for the detection of residual chlorine, since only changes due to the sensing reaction are monitored. Although the device has not been optimized, a potential sensitivity below 1 ppm has been demonstrated. The integration of modem optical technology and electrochemical techniques for sensing applications appears to be a powerful new approach.