Interdigitated Gold Electrodes Research Articles

Moisture-induced power generator fabricated on a lateral field-excited quartz resonator

We fabricated a moisture-induced power generator on a lateral field-excited quartz resonator to simultaneously measure changes in mass and voltage generation during water vapor adsorption. Circularly interdigitated gold electrodes were vacuum deposited on the top surface and used to measure changes in mass, and two symmetric semicircular gold electrodes were vacuum deposited on the bottom surface and used to measure changes in voltage generation. After coating a thin film of a mixture comprising sodium alginate, carbon black, and polyvinyl alcohol (SCP) on the top surface, an electric field was applied to create a concentration gradient of sodium ions between the interdigitated electrodes. The changes in the resonant frequency and voltage generation of the SCP-coated quartz resonator were measured simultaneously under various relative humidity conditions. The results revealed, for the first time, three distinct voltage-generation regions during moisture adsorption: (i) a region of negligible voltage generation, (ii) that of an increase in voltage generation, and (iii) that of a decrease in voltage generation.

Palladium Phthalocyanine Nanowire-Based Highly Sensitive Sensors for NO2(g) Detection.

Palladium phthalocyanine (PdPc) nanowires (NWs) were developed to achieve the gas sensing of NO2 in the sub-parts-per-million (ppm) range. Non-substituted metal phthalocyanine are well known for their p-type semiconducting behavior, which is responsible for its gas-sensing capabilities. Nanofabrication of the PdPc NWs was performed by physical vapor deposition (PVD) on an interdigitated gold electrode (IDE). The coordination of palladium in the structure was confirmed with UV-Vis spectroscopy. Gas-sensing experiments for NO2 detection were undertaken at different sensed gas concentrations from 4 ppm to 0.5 ppm at room temperature. In this work, the responses at different gas concentrations are reported. In addition, structural studies of the PdPc NWs with scanning electron microscopy (SEM) and electron-dispersive X-ray diffraction (EDS) are shown.

Ultrathin Langmuir-Blodgett film of functionalized single-walled carbon nanotubes for enhanced acetone sensing

Acetone is one of the important volatile organic compounds which needs to be detected from the industrial effluent and as a bio-marker from breath of diabetic patients. Here, ultrathin Langmuir-Blodgett (LB) film of octadecylamine- functionalized single-walled carbon nanotubes (ODA-CNT) was formed on interdigitated gold electrodes and was employed for acetone vapor sensing using the impedance spectroscopy (IS) at room temperature. The LB film deposited in liquid-like phase of the Langmuir monolayer of ODA-CNT revealed aligned nanotubes. Being a reducing agent, acetone interacts readily with the CNTs through the transfer of electrons. Using IS, multiparameter were measured with respect to both frequency and acetone vapor concentration. Principal component analysis (PCA) of the IS data revealed capacitance as the most suitable parameter for acetone vapor sensing using the ODA-CNT film. A very low limit of detection (0.5 ppm) and a wide detectable concentration range (1–300 ppm) for acetone sensing using the LB film of ODA-CNT was obtained. The 2D calibration map revealed that the sensing performance of acetone using LB film was much better as compared to that of drop-cast film of ODA-CNT and LB film of pristine CNTs. The superior sensing performance of the LB film of ODA-CNT is attributed to the uniform and aligned nature of the nanotubes, leading to a coherent behavior due to interaction with the acetone molecules. This study shows the potential of LB films of ODA-CNT for sensitive and low level detection of acetone vapor at room temperature.

Lithium salt of a pro-mesogenic [closo-CB11H12]- derivative: anisotropic Li+ ion transport in liquid crystalline electrolytes.

Li+ ion conduction in two aligned liquid crystalline electrolytes consisting of 10 mol% Li+ salt of a pro-mesogenic anion derived from [closo-1-CB11H12]- in non-ionic hosts was investigated. Using electrochemical impedance spectroscopy (EIS), the ionic conductivity in the parallel (σ‖) and perpendicular (σ⊥) directions of the electrolyte samples was determined using two types of cells: an interdigitated gold electrode and a nylon 6-coated ITO cell. The ratio of ionic conductivities σ⊥/σ‖ in the electrolyte with a nona(ethylene oxide) spacer was about 3 in the entire SmA phase, while in the shorter homologue, the ratio monotonically increases from about 0.4 to 2.9. The liquid crystalline behavior of the hosts and the electrolytes was investigated by optical, thermal, and powder XRD methods.

A supersensitive electrochemical sensor based on RCA amplification-assisted “silver chain”-linked gold interdigital electrodes and CRISPR/Cas9 for the detection of Staphylococcus aureus in food

With the rising emphasis on food safety, technology to rapidly identify Staphylococcus aureus (S. aureus) is of great significance. Herein, we developed a novel electrochemical biosensor based on the CRISPR/Cas9 system and rolling circle amplification (RCA)-assisted “silver chain”-linked gold interdigital electrodes (Au-IDE). This sensor utilizes RCA to create DNA long chains that span the Au-IDE, and CRISPR/Cas9 as a recognition component to recognize capture/target dsDNA. Additionally, we used silver staining technology to improve detection sensitivity. Then, we detected S. aureus through impedance changes that occurred when the silver chain between the Au-IDE was connected or broke, with a limit of detection (LOD) of 7 CFU/mL and a detection time of 1.5 h. Lastly, we successfully employed this sensor to detect S. aureus in real food samples, making it a promising tool for food monitoring.

Electro-determination of protonation by tungsten anchored carbon nanoparticle on interdigitated gold electrode

This study presented an enhanced sensitivity of sensing protons (H+) by anchoring tungsten to carbon nanoparticles (WCN) to encourage high current density on the surface of gold interdigitated electrode (AuIDE). The morphology of the sensor evidences the intactness of electrode surface and suitable for WCN modification. To elucidate the study, unmodified AuIDE was compared to the WCN modified surface. Current-volt analysis was compared with electrolyte scouting in the variation of pH by using a picoammater, which supplied 0.0 to 2.0 V with a 0.1 V ramp interval. It was shown that modified WCN gave the sensitivity in the acidic medium (protons) at the pH 4 with a current density value of 2.5 × 10-5 ampere and increased further with lowering the pH to more acidic. This is due to the fact that the tungsten carbon nanoparticle that is anchored offering more electron density and alters the behavior of the chip. Meanwhile, the current density displayed insignificant changes of current density amplification from pH 5 to 12 with the range of 5.91 × 10-9 to 7.36 × 10-8 Ampere. The deposition of WCN on the AuIDE surface chip revealed the successfulness of this nanoparticle in chemically linked with the AuIDE surface and how modified nanoparticle altered the behavior of the sensing element.

An impedance-based chemiresistor for the real-time, simultaneous detection of gut microbiota-generated short-chain fatty acids

Short-chain fatty acids (SCFAs) are key molecules, produced by gut bacteria in the intestine, that are absorbed into the bloodstream and strongly influence human health. SCFA disruption and imbalances have been linked to many diseases; however, SCFAs are seldom used diagnostically as their detection requires extensive sample preparation and expensive equipment. In this work, an electrochemical sensor was developed to enable real-time (requiring less than 2 min per measurement), quantitative measurement of SCFAs from complex samples in liquid phase without the need for extraction, evaporation, or destruction. An impedance-based sensor for in vitro detection of acetic acid, propionic acid, and butyric acid (accounting for more than 85% of SCFAs in the intestine) was fabricated by the deposition of ZnO and polyvinyl alcohol (PVA) on the surface of a microfabricated interdigitated gold electrode. The sensor was first exposed to a broad, physiologically relevant range of concentrations of SCFAs in isolation (0.5–20 mg/ml in electroanalytical cell), and, unlike previously published SCFA sensors that could detect only in gas form with the aid of evaporation, it was able to detect them directly in the liquid phase at room temperature. Subsequently, Electrochemical Impedance Spectroscopy (EIS) analysis was utilized in a complex medium, accompanied by Fe(CN)63−/4−. This was applied to a mixture of SCFAs, prepared in varying ratios and concentrations spanning from 0.5 to 10 mg/ml. The analysis successfully demonstrated the sensor's capacity to accurately measure SCFAs in a mixture of experimental relevance. The recorded faradaic responses were then used to train a fit-to-data model to screen human bacterial isolates and detect which species secrete SCFAs in vitro. This research paves the way for swift, non-destructive assessment of SCFA levels in complex biological samples. The end product is a miniaturized sensor that is highly stable and sensitive, making it ideal for real-time monitoring applications.

Piezoelectric ZnO nanoarrays for catalytic detection of H2O2 with ultra sensitivity

Piezo-electrocatalytic semiconductors with the piezoelectric effect and catalytic properties offer unprecedented opportunities in a variety of applications of chemical sensors, electrocatalysts, and photocatalysis. Herein, we demonstrate a flexible piezo-electrocatalytic sensor based on ZnO nanoarrays for ultrasensitive detection of hydrogen peroxide (H2O2), an important substance in many biologic and medical fields. In situ growth of ZnO nanoarrays on flexible gold interdigital electrodes can effectively couple electrical excitation and external strain-induced piezoelectric polarization to promote catalytic reactions. Therefore, the piezo-electrocatalytic sensor measured by chronoamperometry exhibits an unexpectedly high sensitivity of 487 μA mM−1 cm−2, which is superior to previous results. By using finite element analysis, we simulate the piezoelectric effect of ZnO to elucidate the charge transfer between the strained ZnO and H2O2. This work demonstrates a versatile platform of a flexible piezo-electrocatalytic sensor that can use external mechanical energy to improve chemical and biologic detection.

Interdigitated electrodes-based Au-MoS2 hybrid gas sensor for sensing toxic CO and NH3 gases at room temperature

In the quest to create effective sensors that operate at room temperature, consume less power and maintain their stability over time for detecting toxic gases in the environment, molybdenum disulfide (MoS2) and MoS2-based hybrids have emerged as potent materials. In this context, the current work describes the fabrication of Au-MoS2 hybrid gas sensor fabricated on gold interdigitated electrodes (GIEs) for sensing harmful CO and NH3 gases at room temperature. The GIEs-based Au-MoS2 hybrid sensors are fabricated by decorating MoS2 nanoflowers (MNF) with varying size of Au nanoparticles using an inert gas evaporation technique. It is observed that by varying the size of Au nanoparticles, the crystallinity gets modified, as confirmed by x-ray diffraction and Micro-Raman spectroscopy (μRS). The gas sensing measurements revealed that the best sensing response is found from the Au-MoS2 hybrid (with an average particle size of 10 nm). This particular hybrid shows a 79% response to CO exposure and a 69% response to NH3 exposure. The measurements are about 3.5 and 5 times higher than the bare MoS2 when exposed to CO and NH3 at room temperature, respectively. This enhancement in sensing response is attributed to the modified interfacial interaction between the Au nanoparticles and MNF gets improved, which leads to the formation of a Schottky barrier, as confirmed using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy analysis. This enables the development of efficient gas sensors that respond quickly to changes in the gas around them.

SnO2 nanostructured thin film as humidity sensor and its application in breath monitoring

In the present paper, we studied SnO2 nanostructured thin film-based resistive type humidity sensor fabricated by spin coating method on alumina substrate and showed its application in real time respiratory monitoring. Experiments show the growth of crystalline SnO2 nanoparticles with a tetragonal phase, with an average particle size of ∼15 nm and a high surface roughness of the order of 50-60 nm. The gold-interdigitated electrodes were patterned on the SnO2 film surface by DC sputtering technique to study the sensing response of the film. The sensor shows a high sensitivity of 1.34 kΩ/%RH, a minimal hysteresis of 0.94%, and good repeatability. The developed sensor is tested for monitoring human breath patterns in different physical conditions, and apnea like situations, which suggests its potential for clinical applications. Overall, the present work proposes an environmental friendly, easy-to-synthesize, highly stable, and simple facile SnO2 based deployable humidity sensor to diagnose human health patterns in a non-contact manner.

Highly Sensitive Isopropanol Gas Sensor based on SnO2 Nano-Flowers on Gold, Silver, and Aluminum Interdigitated Electrodes

In this research we have proposed a high selectivity Isopropanol gas sensor. The sensor shows significant resistance change only to Isopropanol gas. The synthesis method of flower-like SnO2 nanostructures, the electrode material and design, and the optimized working temperature provide the high selectivity and high response of the sensor. The SnO2 nanoflowers (NFs) have been synthesized in a two-step process as the gas sensitive layer. The sensor shows its best performance on Au interdigitated electrodes. The optimized working temperature is obtained at 150 °C. The proposed sensor has a high sensitivity, good repeatability, long-term stability and remarkable selectivity. The responses of the sensor to 100 ppm of isopropanol at 150 °C is 71 and the sensor is capable of keeping almost 96% of the initial response in a 40 d period.

Manufacturing of Flexible, Impedimetric Potassium Sensors

In this work, a cost-effective, flexible, and fully printable potassium ion (K+) sensor is developed. The sensor consists of two interdigitated gold electrodes covered by a butylacrylate potassium ion-sensitive membrane (ISM). An impedimetric measurement method is chosen to eliminate the need for a reference electrode and to reduce signal drifting. We show the versatility and high reproducibility of the manufacturing process and present first measurement results. Our sensors achieve a sensitivity of 4.553 MOhm/(mmol/L) at 100 mHz and an accuracy of 1.8 mmol/L. The sensors exhibit low cross-sensitivity towards sodium ions and show no signal drift.

Zr-MOF and PEDOT:PSS composite sensor for chemoresistive sensing of toluene at room temperature

Metal-organic framework (MOF) based composites are advantageous for the development of chemoresistive sensors for gases owing to their high selectivity, sensitivity, and low detection limit. In this study, a composite electrode consisting of Zirconium MOF (UiO-66-NH2) and PEDOT:PSS (Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) was developed for the chemoresistive sensing of toluene. The composite was synthesized via solvothermal route and characterized by various structural and spectroscopic characterizations. The composite was used to prepare a sensor on the interdigitated gold electrode (IDE) platform. A change in the resistance was observed in proportion to the concentration of toluene gas introduced in the sensing chamber. The sensor response was investigated for the toluene concentration varying from 1 to 20 ppm. A sensor response of 1.42 ± 0.14 was achieved for 10 ppm toluene with the average response and recovery times of 362 ± 4 and 106 ± 1 s, respectively. Moreover, the response of the sensor was fairly selective toward toluene as it can tolerate the interference from humidity and some other tested volatile organic compounds. The limit of detection of the sensor was estimated to be 172 ppb. In addition, the sensor exhibited good stability over a period of several days. The fabricated sensor electrode was also confirmed for its repeatability and reproducibility, suggesting its suitability in real-world applications such as air quality monitoring.

Screen-Printed Electrochemical Biosensor for the Detection of Bacteriophage of Lactococcus Lactis for Dairy Production

In the dairy industry, the spreading of phages of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Lactococcus lactis</i> prevent the proper lactic fermentation, causing waste of contaminated products and economic losses. This work presents a cheap biosensing method for rapidly detecting the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L.lactis</i> phages. The detection is based on live <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L. lactis</i> bacteria covering the sensor electrodes, whose electrical response is measured by electrochemical impedance spectroscopy (EIS). Solutions contaminated by phages induce bacteria lysis, clearly reducing the bacteria coverage over the electrodes and leading to evident parametrical shifts in the charge transfer resistance and in the impedance phase at 400 Hz. Experimental tests with laboratory contaminated samples confirm that screen-printed sensors with gold and detection capability compared to interdigitated gold electrodes. Two measurement protocols, called spill-out and drop-in methods, are evaluated to optimize the sensor detection capability and time. The EIS results are compared with optical absorbance measurements at 600 nm, in order to validate the proposed detection method with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> PFU/mL phages and with a detection time of about 5 hours. Lastly, the proposed method is tested successfully with milk-based solutions. Evident shifts are measured in the charge transfer resistance of more than one order of magnitude and impedance phase differences of 43° in phages contaminated sensors.

Development of high-performance broadband optical detector for cryogenic to elevated operating temperature

Development of broadband photodetectors for cryogenic and elevated temperature applications has been a major concern in space science and other radiation detection technologies. With this objective TiS2-nanostructures were investigated for photodetection characteristics in the temperature range of −180 °C to 150 °C. The device was developed by depositing TiS2-nanostructures amid gold-interdigitated electrodes by drop-casting technique. The photodetection performance was investigated for 617 nm and 850 nm LEDs as a function of power density and operating temperature. It is found that as-developed photodetector can operate in the solar spectrum from 375 nm to 1050 nm. The designed photodetector is capable of detecting photons at −180 °C temperature and 0.015 mW/cm2 incident light power density with an ultra-low bias voltage (0.1 V). The operational temperature range can be further extended by optimizing the bias voltage. The device has excellent photodetection capabilities for from sub-zero temperature to elevated temperatures. The highest photocurrent of 45.22 nA is obtained at 617 nm and 0.1 V bias voltage, when the temperature is 0 °C and power density is 0.792 mW/cm2, while the highest values for photoresponsivity (8.9 × 104 A/W), quantum efficiency (1.78 × 105 A/W nm), and detectivity (1.93 × 1014 Jones) are found for 0.015 mW/cm2 power density. Optimization of the Bias-voltage optimization further improves the device performance. At −120 °C operating temperature, the fastest response (response/recovery time∼0.099 s) and highest device ON/OFF ratio of the ‘as-developed’ photodetector are recorded.

Highly Sensitive Ammonia Sensor Based on Modified Nanostructured Polypyrrole Decorated With MAF-6 to Reduce the Effect of Humidity

An ammonia gas sensor based on nanostructured polypyrrole functionalized by carboxylic groups (PPy-COOH) was prepared and characterized. The active layer was deposited on a ceramic substrate with gold interdigital electrodes by a low-cost airbrush-spray coating technique, and the sensor exhibited a strong response to ammonia ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}/{Z}_{{0}}\,\,=$ </tex-math></inline-formula> 5.48 at 100 ppm) in comparison with pure PPy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}/{Z}_{{0}}\,\,=$ </tex-math></inline-formula> 1.5 at 100 ppm). Cross-sensitivity measurement showed a more significant response to relative humidity (RH) and so two approaches were used to reduce this undesirable humidity dependence: 1) the creation of a hydrophobic metal-organic framework (so-called MAF-6) on the PPy-COOH layer and 2) the fabrication of a heterostructure of PPy-COOH with multiwall carbon nanotubes (MWCNTs). Both approaches resulted in a significant reduction in the humidity dependence of the sensor, from the value <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Z}/{Z}_{{0}}\,\,=$ </tex-math></inline-formula> 0.02 (PPy-COOH) to 0.404 and 0.427 for PPy-COOH-MAF-6 and PPy-COOH/MWCNT, respectively. However, the samples coated with MAF-6 showed a smaller decrease in response to ammonia. In addition, the proposed approach with MAF-6 functionalization allowed ammonia detection within a broader RH range (up to 60% RH) compared to the PPy-COOH sensing layer. The presence of MAF-6 on the surface of PPy-COOH was further verified by infrared spectroscopy (FTIR), X-ray diffraction (XRD) spectroscopy, and scanning electron microscopy together with energy-dispersive X-ray spectroscopy (SEM-EDX). The sensing mechanisms of ammonia and RH of the PPy-COOH material are also discussed in this article.

Graphene-Enhanced Screen-Printed BiFeO3-Based Thermistors

In this study, serigraphic-grade BiFeO3-based ink formulations are produced and then mixed with graphene to enhance the performances of screen-printed thermistor devices. The devices are printed atop a standard thermally boosted glass-reinforced epoxy (FR-4) substrate coated with interdigitated gold electrodes. The broader operating temperature range of these thermistors makes them compatible with standard printed circuit board (PCB) manufacturing and operating conditions. Thus, we achieve highly sensitive devices with a temperature coefficient of resistance (TCR) of −0.96%/°C, which is the highest sensitivity reported yet for any graphene-based thermistor operating from 25 to 170 °C. The best-performing devices are loaded with 3.5 wt % graphene. These low-hysteresis and stable thermistors boast a thermal index (β-coefficient) of 864 K. This optimal graphene loading occurs just above the percolation threshold.

Design and Fabrication of a Gas Sensor Based on a Polypyrrole/Silver Nanoparticle Film for the Detection of Ammonia in Exhaled Breath of COVID-19 Patients Suffering from Acute Kidney Injury.

One of the serious complications of COVID-19 is acute kidney injury (AKI), leading to a decrease in kidney function and even death. The concentration of ammonia (NH3) in the exhaled breath (EB) of COVID-19 patients suffering from AKI symptoms will be significantly increased. In this work, the detection of breath NH3 was performed at gold interdigital electrodes modified with a soluble polypyrrole microparticle and silver nanoparticle film (Au-IDEs/S-PPyMPs/AgNPs) as a noninvasive chemiresistor gas sensor. The response behavior of unmodified and modified gas sensors toward NH3 and other interfering compounds was studied. The Au-IDEs/S-PPyMPs/AgNPs exhibited NH3 detection in the linear dynamic range of 1.00-19.23 ppm, with a limit of detection of 0.12 ppm. Finally, the fabricated gas sensor was used to monitor the NH3 concentration in the EB of COVID-19 patients suffering from AKI symptoms. For this purpose, the gas sensor was validated in 19 EB samples (seven COVID-19-positive patients, four COVID-19-negative patients, and eight post-COVID-19 patients). The gas sensor was directly exposed to the EB samples, followed by recording the changes in electrical resistance via a low-cost digital multimeter. The sensing mechanism was explained as the interaction between breath NH3 and sensing materials. The breath NH3 concentrations have a desirable correlation (R2 = 0.8463) with the estimated glomerular filtration rate (eGFR) values in COVID-19-positive patients. The fabricated gas sensor can distinguish COVID-19-positive patients suffering from AKI symptoms from COVID-19-negative patients and post-COVID-19 patients. The present work can pave the way for the development of a simple and efficient analytical approach for COVID-19 patients with AKI without the need for sample pretreatment.

Enhanced Room-Temperature Ethanol Detection by Quasi 2D Nanosheets of an Exfoliated Polymeric Graphitized Carbon Nitride Composite-Based Patterned Sensor.

A novel room-temperature gas sensor composed of polymeric graphitic carbon nitride composite was fabricated and used for the detection of ethanol vapor under ambient conditions. Polymeric carbon nitride (PCN) microstructures composed of fluffy nanosheets were synthesized via a thermal polycondensation mechanism using melamine as the precursor, followed by vigorous chemical exfoliation. These sheet-like microstructures were employed as active materials in the form of composites, along with carbon paste consisting of graphite nanoplatelets and carbon black. The active sensing layer was fabricated on a PET sheet and assembled on an interdigitated gold electrode. The as-fabricated sensor exhibited excellent sensing efficiency (>100% response at 10 ppm) along with high selectivity and stability. In particular, for ultralow concentrations such as 1 ppm (>10% response), this resistive-based sensor exhibited a swift response time provided under ambient conditions. The exfoliated PCN composite sensor was found to be working with appreciable efficiency at moderate relative humidity (%) with the least fluctuation in response signals also demonstrating long-term stability for 30 days with consistent response signals.

Probing the Influence of Crosslinking Layer Incubation Time on the Performance of Non-Faradaic Impedimetric Biosensors

Non-faradaic impedimetric biosensors have received a wide interest due to their direct detection approach. The crosslinking layer in these biosensors has to be dense to avoid permeation of ions into the electrode to allow direct detection of diseases. In this work, we investigate, for the first time, the effect of incubation time of cysteamine crosslinking layer on non-faradaic impedimetric biosensors performances. Two sets of interdigitated gold electrodes were functionalized with cysteamine for 1 h and 24 h. Then, UL83-antibodies were immobilized on the surface via glutaraldehyde for the detection of human cytomegalovirus. The sensitivity of biosensors functionalized with cysteamine for 24 h were superior to those functionalized with cysteamine for 1 h (i.e. 0.046 nF/ln(ng ml−1) compared to 0.0224 nF/ln(ng ml−1)). Probing the cysteamine layer with faradaic-EIS and X-ray photoelectron spectroscopy suggests that the better biosensing performance of biosensors incubated in cysteamine for 24 h is related to the better coverage of cysteamine at the biosensor surface. Atomic force microscopy analysis also revealed an increase in surface roughness with increasing cysteamine incubation time which resulted in better biosensing performances due to the enlarged surface area.