A capacitive field-effect sensor for the direct determination of organophosphorus pesticides

doi:10.1016/S0925-4005(03)00071-6

Sensors and Actuators B: Chemical

Volume 91, Issues 1–3, 1 June 2003, Pages 92-97

https://doi.org/10.1016/S0925-4005(03)00071-6 Get rights and content

Abstract

A novel capacitive field-effect sensor for the direct determination of organophosphorus pesticides by the enzyme organophosphorus hydrolase (OPH) is presented. The enzyme OPH hydrolyses organophosphorus compounds catalytically, thus releasing H⁺ ions. By means of a silicon-based field-effect sensor, which consists of a layer sequence of Al/p-Si/SiO₂ with alternative pH-sensitive materials (Ta₂O₅, Al₂O₃ and Si₃N₄), this pH shift can be recorded directly in a potentiometric measuring arrangement. To obtain the enzyme biosensor, thus the OPH has been immobilised on top of the pH-sensitive layer structure. Typical sensor characteristics, like pH sensitivity, sensitivity towards paraoxon, reversibility of the sensor signal, response time, detection limit, long-term stability and selectivity to various pesticides have been studied.

Introduction

Synthetic organophosphorus compounds—among the most toxic substances known—are used as pesticides or insecticides in agriculture and chemical warfare agents. Biosensors to detect these neurotoxins, has been an actively researched area. The majority of biosensors to date is based on the inhibition of acetylcholinesterase or butyrylcholinesterase integrated with electrochemical (potentiometric and amperometric) and optical transducers [1], [2], [3]. Although sensitive, these biosensors suffer from several limitations: poor selectivity, multi-step indirect determination, and irreversible inhibition by many compounds, to name a few. Recently, we have demonstrated the application of another enzyme, generically termed organophosphorus hydrolase (OPH), as the biological recognition element for various biosensors. This enzyme catalyses the hydrolysis of organophosphates (OPs) after releasing products that can be monitored. We have integrated this enzyme with a number of different transducers to develop biosensors that allow rapid, selective, sensitive and on-line determination of OPs [3]. Taking advantage of the fact that hydrolysis of OPs by the OPH releases proton(s), we reported a simple potentiometric biosensor in which OPH was integrated with a glass pH electrode [4]. In order to miniaturise the potentiometric biosensor, OPH was immobilised at the gate of a pH-sensitive field-effect transistor (ISFET) [5]. However, the application of miniaturised ISFET-type sensors leads to several disadvantages: instability of the required passivation layer when in permanent contact with the test sample (or electrolyte), high costs of fabrication due to photolithographical process steps, etc.

To overcome these problems, we suggest the application of a simple capacitive electrolyte–insulator–silicon (EIS) field-effect structure as transducer of an OPH-based biosensor. The layer set-up of this EIS sensor corresponds to the gate region of an ISFET, however, due to the missing photolithographic process steps, no additional passivation and encapsulation layer of the sensing area is necessary. The sensor can be easily mounted in a home-made Plexiglas cell, e.g. sealed by an O-ring. Thus, this transducer structure possesses a higher stability in the long-term than ISFET-based transducer structures and is much more cheaper in sensor preparation [6].

In this paper, a novel EIS-based sensor for the direct determination of organophosphorus pesticides by the enzyme OPH is presented. For the transducer structure, three alternative pH-sensitive materials Ta₂O₅, Al₂O₃ and Si₃N₄ have been used. Whereas the Ta₂O₅ and Al₂O₃ layers are grown by means of pulsed laser deposition (PLD), Si₃N₄ has been deposited by low pressure chemical vapour deposition (LPCVD) onto a basic structure of Al/p-Si/SiO₂. To achieve the capacitive EIS biosensor, OPH has been immobilised by three different strategies on top of the pH-sensitive layer structure: (1) by covalent coupling via glutaraldehyde; (2) by cross-linking with nafion; and (3) by an adsorptive technique. Depending on the immobilisation procedure used and the pH-sensitive material applied, typical sensor characteristics, like pH sensitivity of the transducer material before and after the enzyme immobilisation, the biosensor performance towards paraoxon including the linear concentration range, the reversibility of the biosensor signal, the response time as well as the detection limit and the biosensor stability in the long-term have been investigated; the selectivity to various pesticides will be discussed.

Section snippets

Materials and processing

The different EIS structures of the layer sequences Al/p-Si/SiO₂/Al₂O₃, Al/p-Si/SiO₂/Ta₂O₅ or Al/p-Si/SiO₂/Si₃N₄ were fabricated from p-type Si (18–24 Ω cm, Wacker Chemitronic) with <1 0 0> orientation. A SiO₂ layer of 30 nm has been grown by means of thermal oxidation. For the preparation of the pH-sensitive materials Al₂O₃ and Ta₂O₅ (thickness: 30–50 nm), respectively, the PLD process has been employed, whereas the LPCVD technique was used to deposit the Si₃N₄ layer. The Al rear contact has been

Results and discussion

Fig. 3 shows a typical C/V curve of a capacitive field-effect sensor with Si₃N₄ as pH-sensitive material in buffer solution, pH 7, before (full line) and after modification of the Si₃N₄ surface by OPH enzyme deposited by cross-linking (open squares). The maximum capacitance in the accumulation range is about 45 nF. Both curves indicate a nearly identical behaviour in terms of signal shape and capacitance values. The slight deviations are probably due to small variations in the additional

Conclusions

For future research studies, the developed biosensor should be integrated in a flow-injection analysis system to demonstrate its availability for real sample monitoring. The combination of a potentiometric with an amperometric sensor, for example, will improve the sensitivity and selectivity characteristics. Both sensors can be integrated as hybrid on a single chip. In such a dual biosensor chip, the amperometric detection principle is relied on the amperometric determination of para

Acknowledgements

The authors gratefully thank F. Johnen and J. Schubert for technical support. Part of the work has been funded by the Ministerium für Schule, Wissenschaft und Forschung des Landes Nordrhein-Westfalen, the US Environmental Protection Agency (R823663-01-0, R82816001-0), the US Department of Agriculture (99-35102-8600) and the National Science Foundation (BES 9731513).

References (14)

C. Ristori et al.
Potentiometric detection of pesticides in water samples
Anal. Chim. Acta
(1996)
A. Mulchandani et al.
Biosensors for direct determination of organophosphate pesticides
Biosens. Bioelecton.
(2001)
P. Mulchandani et al.
Biosensor for direct determination of organophosphate nerve agents. Part 1. Potentiometric enzyme electrode
Biosens. Bioelectron.
(1999)
A.K. Singh et al.
Development of sensors for direct determination of organophosphates. Part I. Immobilization
Biosens. Bioelecton.
(1999)
M.J. Schöning et al.
A highly long-term stable silicon-based pH sensor fabricated by pulsed laser deposition technique
Sens. Actuators B
(1996)
M.J. Schöning et al.
Can pulsed laser deposition serve as an advanced technique in fabricating chemical sensors?
Sens. Actuators B
(2001)
M. Thust et al.
A long-term stable penicillin-sensitive potentiometric biosensor with enzyme immobilized by heterobifunctional cross-linking
Anal. Chim. Acta
(1996)

There are more references available in the full text version of this article.

Cited by (40)

Smartphone-assisted colorimetric biosensor for the determination of organophosphorus pesticides on the peel of fruits
2024, Food Chemistry
Nowadays, the widespread use of organophosphorus pesticides (OPs) in agricultural production leads to varying degrees of residues in crops, which pose a potential threat to human health. Conventional methods used in national standard for the detection of OPs in fruits and vegetables require expensive instruments or cumbersome sample pretreatment steps for the analysis. To address these challenges, in this work, we took advantage of the peroxidase-like activity of PtCu₃ alloy nanocrystals (NCs) for a colorimetric and smartphone assisted sensitive detection of OPs. With the assist of a smartphone, the concentration of OPs on the peel of fruits could be obtained by comparing the B/RG value (the brightness value of blue divided by those of red and green) of a test strip with a calibration curve. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety warning.
Rapid analysis of dichlorvos via releasing the phosphate core
2024, Talanta
Monitoring the residual dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate, DDVP) in food has received extensive attention owing to its large consumption in agriculture. However, the previous sensing methods are not time-efficient enough due to the long incubation time for enzyme inhibition (tens of minutes to hours) or bottlenecked by the complicated procedures for senor fabrication. Herein, a novel sensing strategy is proposed based on the hydrolysis of DDVP into PO₄³⁻. By using alkaline phosphatase for hydrolysis, a certain portion of DDVP was transformed to PO₄³⁻ within only 8 min. Then, the released PO₄³⁻ was detected by a fluorescent terbium metal-organic framework (Tb-MOF). The coordination of the naked P–O groups to the metal nodes of the Tb-MOF disturbed the antenna effects of its ligands. Thus, DDVP was quantified by the decrease of the fluorescence of Tb ions. Based on this method, DDVP residues on plum surfaces were collected by swabs and successfully detected. The recovery of DDVP was determined in the range from 105 % to 115 %, demonstrating the quantification accuracy of this method. The detection limit reached 4.7 μM, which was lower than the restricted amount in fruit set by the National Standard of China. The present method provides an efficient and user-friendly way for the detection of DDVP and many other organophosphorus pesticides in food.
Current state and future prospects of sensors for evaluating polymer biodegradability and sensors made from biodegradable polymers: A review
2022, Analytica Chimica Acta
Citation Excerpt :
Capacitive field-effect sensors comprising electrolyte-insulator-semiconductor (EIS) have been recognized as useful sensing devices for biodegradable polymer analysis [51,52]. The EIS sensors efficiently detected various parameters, including pH and concentration of charged macromolecules (e.g., polyelectrolytes and DNA), metal ions, and penicillin [53–55]. The EIS sensors consist of a gate-insulator (SiO2–Ta2O5) formed on a semiconductor substrate, i.e., p-silicon, and a contact layer on the backside (e.g., aluminum).
Since the invention of fully synthetic plastic in the 1900s, plastics have been extensively applied in various fields and represent a significant market due to their satisfactory properties. However, the non-biodegradable nature of most plastics has contributed to the accumulation of plastic waste, which poses a threat to both the environment and living beings. Given this, biodegradable polymers have emerged as eco-friendly substitutes for non-biodegradable polymers, and standard test methods have been established to evaluate polymer biodegradability. Technological advancement and the weaknesses of conventional test methods drive the invention of sensors that enable real-time monitoring of biodegradability. Besides, biodegradable polymers have been utilized to make sensors with different functionalities. Given this, the current paper is the first to compare and contrast sensors capable of identifying biodegradable polymers. The detection using sensors represents an innovative perspective for real-time monitoring of biodegradability. Besides, sensors made from biodegradable polymers are included, and these sensors are of different types and show various applications. Finally, the challenges associated with developing these sensors are described to advance future research.
Demonstration of the enhancement of gate bias and ionic strength in electric-double-layer field-effect-transistor biosensors
2021, Sensors and Actuators, B: Chemical
Citation Excerpt :
In comparison with complex large equipments for biomarker detection, FET-based biosensors have unique advantages such as high sensitivity, fast response and low cost, attracting a great interest in recent years [1–4]. Signal transduction and amplification are generally gated by biomolecule interaction, and a variety of targets can be detected by immobilizing different receptors such as antibodies, nucleic acids, enzymes, and even whole cells on the FET gate region [5–11]. The mechanism of conventional FET biosensors relies on charge accumulation resulted from target-receptor binding.
In this study, we investigate the mechanism of enhanced electric-double-layer (EnEDL) field-effect-transistor (FET)-based biosensors, which can successfully detect proteins in high ionic strength solution, such as in 1XPBS. This EnEDL FET biosensor performs good sensitivity in high ionic strength solution by creating enhanced capacitance in the EDL with higher gate voltage or higher salt concentration, and operating in a large transconductance of the FET to amplify the signal. AC impedance measurement is also introduced and identifies that the imaginary part dominates the sensitivity of C-reactive protein (CRP) detection, indicating that the EnEDL capacitance plays the key role in the sensing mechanism. Extended gate connecting to the FET and a separated gate electrode is fabricated and biased with the gate voltage for the EnEDL FET biosensors. The test solution is placed between the two electrodes, and the voltage drop across the solution caused by CRP concentration was analyzed for different gate voltages and salt concentrations for the EnEDL FET biosensors. The results show that as the EDL is enhanced by higher gate bias or higher salt concentration, the sensitivity is increased, either in AC impedance analysis or voltage drop in the test solution. To utilize the enhanced EDL, the maximum transconductance of the FET should be located in a larger gate voltage. This technology can allow direct protein detection in 5 min. without complex dilution of clinical samples, which is promising for portable devices for personal healthcare.
Bio-sensing of organophosphorus pesticides: A review
2019, Biosensors and Bioelectronics
Organophosphorus (OP) pesticides have been used widely as agricultural and household pest control agents for almost five decades and persist in our water resources, fruits, vegetables and processed food as health and environmental hazardous compounds. Thus, detection of these harmful OP pesticides at an ease with high sensitivity and selectivity is the need of hour. Bio-sensing technology meet these requirements and has been employed at a large scale for detection. The present review is aimed mainly to provide the overview of the past and recent advances occurred in the field of biosensor technology employed for the detection of these OP compounds. The review describes the principle and strategy of various OP biosensors including electrochemical (amperometric, potentiometric), thermal, piezoelectric, optical (fluorescence, Surface Plasmon Resonance (SPR)), microbial and DNA biosensors in detail. The electrochemical biosensors are generally, based on inhibition of enzyme, acetyl cholinesterase (AChE), butyryl cholinesterase (BChE), tyrosinase and alkaline phosphatase or enzyme (organophosphorus hydrolase, OPH)) catalyzed reaction. The detection limits and linearity range of various OP biosensors have also been compared. AChE inhibition based amperometric OP biosensors exhibited the lowest detection limit of 1 × 10⁻¹¹ μM with a linearity range of 1.0 × 10⁻¹¹ – 1.0 × 10⁻² μM.
Low-cost top-down zinc oxide nanowire sensors through a highly transferable ion beam etching for healthcare applications
2016, Microelectronic Engineering
Citation Excerpt :
Therefore, by selecting a reference current (Iref), the effect of pH change can be measured by evaluating the liquid gate voltage (Vlg) shift at this reference current as shown in Fig. 6b. It can be seen that the voltage shift has a linear relation with pH values between 3 and 9, and the per pH voltage shift can be extracted from the plot to be 46.5 mV/pH. This voltage shift closely follows the literature values for an Al2O3 surface on nanowire sensors [13,14]. Fig. 6c shows bottom-gate subthreshold (Id–Vb) characteristics of a typical sensor when different pH buffers were applied.
In this work, we demonstrate a wafer-level zinc oxide (ZnO) nanowire fabrication process using ion beam etching and a spacer etch technique. The proposed process can accurately define nanowires without an advanced photolithography and provide a high yield over a 6-inch wafer. The fabricated nanowires are 36 nm wide and 86 nm thick and present excellent transistor characteristics. The pH sensitivity using a liquid gate was found to be 46.5 mV/pH, while the pH sensitivity using a bottom gate showed a sensitivity of 366 mV/pH, which is attributed to the capacitance coupling between the top- and bottom-gates. The maximum process temperature used in the fabrication of the nanowire sensors is optimized to be 200 °C (after wet oxidation) which makes it applicable to low-cost substrates such as glass and plastic. The Ion Beam Etching (IBE) process in this work is shown to be highly transferable and can therefore be directly used to form nanowires of different materials, such as polysilicon and molybdenum disulfide, by only an adjustment of the etch time.

View all citing articles on Scopus

¹: Co-corresponding author.

View full text