Label-free Impedimetric Biosensor Research Articles

Phage probe on RAFT polymer surface for rapid enumeration of E. coli K12

This study presents a simple, fast, and sensitive label-free sensing assay for the precise enumeration of modeled pathogenic Escherichia coli K12 (E. coli K12) bacteria for the first time. The method employs the covalent binding bacteriophage technique on the surface of a reversible addition-fragmentation chain transfer (RAFT) polymer film. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) identified the charge transfer resistance Rct was calculated from a suitable electrochemical circuit model through an evaluation of the relevant parameter after the immobilization of the bacteriophage and the binding of specific E. coli K12. The impedimetric biosensor reveals specific and reproducible detection with sensitivity in the linear working range of 104.2-107.0 CFU/mL, a limit of detection (LOD) of 101.3 CFU/mL, and a short response time of 15 min. The SERS response validates the surface roughness and interaction of the SERS-tag with E. coli K12-modified electrodes. Furthermore, the covalently immobilized active phage selectivity was proved against various non-targeting bacterial strains in the presence of targeted E.coli K12 with a result of 94 % specificity and 98 % sensitivity. Therefore, the developed phage-based electrode surface can be used as a disposable, label-free impedimetric biosensor for rapid and real-time monitoring of serum samples.

Label-free impedimetric biosensor based on a novel DNA-type receptor for selective determination of lactoferrin in human saliva

We propose a new impedimetric biosensor utilizing a unique H2N-(CH2)6-5’[TAGAGGATCAAA-AAA]4TAGAGGATCAAA3’ dsDNA oligonucleotide as a biorecognition element for selective lactoferrin determination in human saliva. The spatial orientation of the biosensing layer was defined by the immobilization of dsDNA oligonucleotide via H2N- group at 5’ end. The fabricated biosensors were characterized using both faradaic and non-faradaic models and proposing the Randles-based electrical equivalent circuits. Analysis of experimental data employing faradaic model equivalent circuits revealed a charge transfer resistance parameter R3 f dependent on the lactoferrin concentration. Hence, the biosensor response was established as the relationship between the ratio before/after bioreceptor-analyte interaction and the analyte concentration. The linear response of the developed impedimetric biosensors for laboratory samples was in the lactoferrin concentration range up to 625 nM with limit of detection of 1.25 nM. Notably, this study marked the pioneering application of these biosensors for quantitative lactoferrin detection in human saliva samples. The results exhibited accordance with the surface plasmon resonance method utilizing the same DNA-type receptor applied and colorimetric immunoassay. The presented impedimetric DNA-based biosensor for lactoferrin addresses the pressing need for rapid, simple, and effective analytical methods of immunomodulators detection with applicatory potential in clinical diagnosis.

Bacteriophage-based nano-biosensors for the fast impedimetric determination of pathogens in food samples

The early and rapid detection of pathogenic microorganisms is of critical importance in addressing serious public health issues. Here, a new bacteriophage-based nano-biosensor was constructed and the electrochemical impedimetric method was fully optimized and applied for the quantitative detection of Escherichia coli O157:H7 in food samples. The impact of using a nanocomposite consisting of gold nanoparticles (AuNPs), multi-walled carbon nanotubes (MWCNTs), and tungsten oxide nanostructures (WO3) on the electrochemical performance of disposable screen printed electrodes was identified using the cyclic voltammetry and electrochemical impedance spectroscopy. The use nanomaterials enabled high capturing sensitivity against the targeting bacterial host cells with the limit of detection of 3.0 CFU/ml. Moreover, selectivity of the covalently immobilized active phage was tested against several non-targeting bacterial strains, where a high specificity was achieved. Thus, the targeting foodborne pathogen was successfully detected in food samples with high specificity, and the sensor provided an excellent recovery rate ranging from 90.0 to 108%. Accordingly, the newly developed phage-biosensor is recommended as a disposable label-free impedimetric biosensor for the quick and real-time monitoring of food quality.

A Simple and Low-Cost Electrochemical Immunosensor for Ultrasensitive Determination of Calreticulin Biomarker in Human Serum.

An early on time detection of breast cancer significantly affects the treatment process and outcome. Herein, a new label-free impedimetric biosensor is developed to determine the lowest change in the level of calreticulin (CALR), which is a new biomarker of breast carcinoma. The proposed immunosensor is fabricated by using reduced graphene oxide/amino substituted polypyrrole polymer (rGO-PPyNH2 ) nanocomposite modified disposable electrode. The anti-CALR antibodies are first attached on the rGO-PPyNH2 nanocomposite coated electrode through glutaraldehyde crosslinking; the CALR antigens are then immobilized with the addition of CALR antigens to form an immunocomplex on the sensing surface. This immunocomplex induces considerably larger interfacial electron transport resistance (Rct ). The variation in the Rct has a linear relationship with CALR level in the detection range of 0.025 to 75pg mL-1 , with a detection limit of 10.4 fg mL-1 . The suggested biosensor shows high selectivity to CALR, good storage stability (at least 5 weeks) and suitable reproducibility results as shown in quality control chart. The designed immunosensor is utilized to analyze CALR levels in human sera with satisfying results. This immunosensor provides a novel way for the clinical determination of CALR and other cancer biological markers.

Split aptamers immobilized array microelectrodes for detection of chlorpyrifos pesticide using electrochemical impedance spectroscopy

Pesticide contamination in foods and its high persistence in environments are major serious issues globally. Chlorpyrifos (CPS), a broad-spectrum organophosphate insecticide, is commonly used as an active ingredient for pest control in agricultures and industries, and eventually it is found in high prevalence of contamination in food chains. Unfortunately, CPS exerts several adverse effects, especially as a neurotoxic agent, that cause severe health implications on humans and animals. To prevent the overexposure of pesticide residues in contaminated foods and environments, a label-free impedimetric aptamer-based biosensor for CPS determination was developed. The split aptamers for CPS were designed from its parent sequence to encounter nonspecific binding, and were immobilized onto the array microelectrodes consisting of four gold (Au) working microelectrodes, a platinum (Pt) counter microelectrode, and two Ag/AgCl reference microelectrodes. The aptasensor showed a good linear EIS response with CPS concentration ranging from 0.01 to 1 μg/mL with a detection limit (LOD) of 0.01 μg/mL. Moreover, the aptamer-immobilized Au multi-microelectrodes provided excellent selectivity to CPS over high level of other interferences, yet it also revealed good reproducibility. The sensitivity of CPS was successfully determined with acceptable recoveries in the range of 75–128% in spiked coriander, orange juice, and tap water. Therefore, the split aptamer-functionalized microchip could be a potential biosensor for monitoring CPS contamination in fruits, vegetables, and environments to improve human health and well-being.

A multipurpose biocapture nanoplatform based on multiwalled-carbon nanotubes non-covalently functionalized with avidin: Analytical applications for the non-amplified and label-free impedimetric quantification of BRCA1

We introduce an innovative and versatile multipurpose biocapture nanoplatform made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with avidin (Av) as support to immobilize a biorecognition element just by mixing them in solution. As proof-of-concept of the advantages of this platform, we propose a non-amplified and label-free impedimetric BRCA1 biosensor prepared by immobilization of a biotinylated DNA probe (bDNAp) at MWCNTs-Av nanoplatform and further deposition of the resulting biosensing layer at glassy carbon (GCE) or screen printed carbon (SPCE) electrodes. The hybridization event was detected from the changes in the charge transfer resistance (Rct) of [Fe(CN)6]3-/4-. The resulting genosensor made possible the fast, highly sensitive and selective quantification of BRCA1 in a simple way, with a linear range between 1.0 fM and 10 nM, a sensitivity of (460 ± 9) ΩM−1 (r2 = 0.997), a detection limit of 330 aM and a quantification limit of 1.0 fM. The reproducibility was 5.2% and 4.6% for 1.0 × 10−12 M and 1.0 × 10−14 M BRCA1, respectively, using the same MWCNTs-Av-bDNAp platform, and 5.2% for 1.0 × 10−12 M BRCA1 using 5 different platforms. The biosensor was challenged with fully non-complementary and mismatch DNA sequences, and mixtures of them, without interference. The detection of BRCA1 in enriched diluted human serum samples showed excellent recovery percentages.

Selection of Highly Specific Aptamers by Graphene Oxide-SELEX to Ultrasensitive Label-Free Impedimetric Biosensor Development for Glyphosate Detection

Selection of Highly Specific Aptamers by Graphene Oxide-SELEX to Ultrasensitive Label-Free Impedimetric Biosensor Development for Glyphosate Detection

Probeless and label-free impedimetric biosensing of D-dimer using gold nanoparticles conjugated with dihexadecylphosphate on screen-printed carbon electrodes

D-dimer (DD) is a clinical biomarker of emerging significance. Its fast analysis and quantification, preferably by the bedside, helps a medical doctor make crucial decisions. Electrochemical biosensors are point-of-care technologies that can address such issues. Herein, it is developed a probeless and label-free impedimetric DD biosensor. Gold nanoparticles (AuNPs) are dispersed along with dihexadecylphosphate (DHP) on the surface of screen-printed carbon electrodes (SPCEs) to attach anti-DD monoclonal antibody as sensing recognition element, and the measurements are performed using electrochemical impedance spectroscopy (EIS). Two different analytical models are used to interpret raw impedance spectra. The first model is based on the capacitive response within the DHP monolayer and its electrochemical occupancy described by the complex capacitance value at the frequency of 200 mHz, noted as M1. The second model is based on the charge transfer resistance changes (Rct) occurring upon the mAb-DD binding event, fitted by two different Randles types of the equivalent circuits (noted as M2a and M2b). The models are compared, and with the obtained high linearity in the clinically relevant range (up to 500 ng mL−1) and low levels of detection (as low as 8.92 ng mL−1), a potential POC sensor is demonstrated. Additionally, the proposed sensor is applied in real whole blood samples showing good recovery values with certain discrepancies from the standard laboratory assay result, making a cheap and straightforward way for semi-quantitative bedside clinical evaluation.

A sensitive label-free impedimetric DNA biosensor based on silsesquioxane-functionalized gold nanoparticles for Zika Virus detection

Zika virus (ZIKV) has recently become a global health challenge due to its rapid geographical expansion, since it is associated with serious neurological anomalies such as Guillain-Barré syndrome and microcephaly. Currently, the techniques for ZIKV diagnosis require labor-intensive, expensive and lengthy tests using sophisticated equipment. Moreover, false-positive or false-negative results can occur. In the present work, a DNA biosensor to detect ZIKV in real human serum samples was developed using an oxidized glassy carbon electrode (ox-GCE) modified with silsesquioxane-functionalized gold nanoparticles (AuNPs-SiPy). This nanohybrid was characterized by UV-Vis, FTIR and Raman spectroscopies, DLS, and XRD. The conditions for the immobilization of a ZIKV ssDNA probe on the electrode surface (ox-GCE-[AuNPs-SiPy]) were optimized by univariate and multivariate analysis. The optimized biosensor was characterized by CV, EIS and AFM experiments. The ZIKV target recognition was based on the variation of the charge transfer resistance (ΔRct) of the redox marker ([Fe(CN)6]3-/4-) used and the roughness (Rq) of the electrode surface. The proposed biosensor presented a LOD of 0.82 pmol L-1, with a linear range of 1.0 x10-12 – 1.0 x10-6 mol L-1. Moreover, the reported device showed a suitable stability and satisfactory sensitivity and selectivity to quantify ZIKV in human serum samples, which suggests its promising clinical applications for the early diagnosis of ZIKV-associated pathologies.

Flexible Biosensors for the Impedimetric Detection of Protein Targets Using Silk-Conductive Polymer Biocomposites.

To expand the applications of flexible biosensors in point-of-care healthcare applications beyond monitoring of biophysical parameters, it is important to devise strategies for the detection of various proteins and biomarkers. Here, we demonstrate a flexible, fully organic, biodegradable, label-free impedimetric biosensor for the critical biomarker, vascular endothelial growth factor (VEGF). This biosensor was constructed by photolithographically patterning a conducting ink consisting of a photoreactive silk sericin coupled with a conducting polymer. These functional electrodes are printed on flexible fibroin substrates that are controllably thick and can be free-standing, or conform to soft surfaces. Detection was accomplished via the antibody to VEGF which was immobilized within the conducting matrix. The results indicated that the developed flexible biosensor was highly sensitive and selective to the target protein, even in challenging biofluids such as human serum. The biosensors themselves are biocompatible and degradable. Through this work, the developed flexible biosensor based on a simple and label-free strategy can find practical applications in the monitoring of wound healing or early disease diagnosis.

Electrochemical detection of plant virus using gold nanoparticle-modified electrodes

Tristeza is one of the destructive diseases of citrus causing by citrus tristeza virus (CTV). Historically, CTV has been associated with serious outbreaks of quick decline of citrus, therefore CTV monitoring is important aspect for avoiding such re-emerging epidemics, which would threat citrus production through the world. In this context, we have designed for the first time a label-free impedimetric biosensor for the detection of nucleic acid of CTV. The sensing platform based on a screen-printed carbon electrode (SPCE) was modified by electrodeposited gold nanoparticles (AuNPs), which allowed to efficiently immobilizing thiolated ssDNA probes as well to enhance the electrode conductivity. The growth of AuNPs was optimized and characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We investigated the behavior of thiolated ssDNA probe layer and its hybridization with target DNA onto AuNP surfaces by EIS measurements in Fe(CN6)4-/Fe(CN6)3- red-ox system. The main sensor design aspects such as AuNPs size, probe DNA concentration and immobilization time together with DNA hybridization time were optimized so as to achieve the best performance. Impedance values of DNA hybridization increased with Citrus tristeza-related synthetic DNA concentration, showing a logarithmic relation in the range of 0.1–10 μM. The results also indicate that the biosensor was able to selectively detect CTV nucleic acids in the presence of other non-specific DNAs. Moreover, we have demonstrated the good performance of the system in a real plant sample matrix. In addition, the sensor reproducibility enhanced after the hybridization onto MCH/poly (AT) thiolated DNA probes which was confirmed by intra- and inter-day variability assays.

Impedimetric biosensor for detection of cancer cells employing carbohydrate targeting ability of Concanavalin A

The successful development of selective detection of cancer cells from normal cells is a highly demanded but challenging task. Herein, we have developed a rapid and label-free impedimetric biosensor for quantitative determination of cancer cells with high glycoprotein expression. Homogenously distributed 2–9 nm graphene quantum dots (GQDs) was anchored on the surface Fe3O4 through covalent bonding. Concovalin A (ConA) was then adhered onto GQDs by physical mixing to fabricate ConA-GQD@Fe3O4 nanosensing probe. A good dynamic range in the cell concentration of 5 × 102–1 × 105 cells mL-1 with LOD values of 246 and 367 cells mL-1 for HeLa and MCF-7, respectively, is obtained. The impedimetric responses to the cancerous HeLa and MCF-7 cells are 16.7 and 13.1 times higher than those of their original sensor electrodes. However, the interaction between sensing probe and normal MCF-10 and bEnd.3 cells is negligible, confirming the specific selectivity toward cancer cells. Cellular uptake images as well as in-vitro cytotoxicity corroborates the electrochemical results. In addition, the successful detection of cancer cells in human serum and circulating tumor cells in blood sample envisions the feasibility of using ConA-GQD@Fe3O4 as the nanosensing probe for clinically early diagnosis of cancer cells with high glycoprotein expression.

Impedimetric gene assay for BCR/ABL transcripts in plasmids of patients with chronic myeloid leukemia.

A label-free impedimetric biosensor was developed for determination of BCR/ABL transcripts. Specific DNA primers were covalently immobilized on a gold electrode modified with carboxylated multiwalled carbon nanotubes (cMWCNTs) and zinc oxide nanoparticles (ZnO-NPs). Aggregation of the ZnO-NPs is prevented by the introduction of an amino-modified silica coating, which also allows a subsequent covalent linkage to cMWCNTs. The impedimetric biosensor was typically operated at a working voltage of +10mV vs. Ag/AgCl, in a frequency range from 100 mHz to 100kHz. Studies on the surface morphology and electrochemical properties of the electrode demonstrated improved bioactivity. Amperometric currents and impedimetric parameters, such as charge transfer resistance, varied significantly throughout the construction of the biosensor. The hybridization process was also evidenced by changes in the topography of the surface after exposure to samples containing BCR/ABL. The gene sensor has a linear concentration range for the target gene of 6.94 aM to 694 fM with a limit of detection as low as 0.039 aM. Also, the biosensor is selective and reproducible with a standard deviation of 4.1%. Three replicates for each experimental condition were used. Hence, it is perceived to be a viable tool for early-stage diagnosis of the BCR/ABL fusion gene and monitoring of major molecular remission in clinical samples. Graphical abstract Schematic of a highly sensitive hybridization assay for theBCR/ABL fusion gene. It is based on ZnO nanoparticle functionalized with 3-(aminopropyl)triethoxysilane.

Label-free impedimetric glycan biosensor for quantitative evaluation interactions between pathogenic bacteria and mannose

In order to understanding the pathogenic mechanism of infectious diseases, it was important to study the selective recognition and interaction between pathogenic bacteria and host cells. In this paper, a novel electrochemical impedance biosensor was proposed, in which the Man/MUA-MH/Au sensing surface (Man: mannose; MUA: 11-mercapto eleven acid; MH: 6-mercapto hexanol) was fabricated and was of good biologically active and stability. The capture capacity of the designed sensing surface for S. typhimurium ATCC14028, E. coli JM109 and E. coli DH5α were characterized by Electrochemical impedance spectroscopy (EIS). According to Randless equivalent circuit and the Frumkin isotherm model, electron transfer impedance (Ret) was obtained and the binding affinity of the three bacteria and Man was calculated. It was shown that the sensing surface had a better binding affinity for S. typhimurium ATCC14028 with KADS(S.T.) = 2.16 × 106 CFU/mL. The impedance normalized value NIC (S.T.-Man) was of a good linear relationship with the logarithm of bacterial concentration (R2 = 0.96) in the range of 50–1000 CFU/mL. The detection limit was 50 CFU/mL. Meanwhile, the E. coli JM109 which expresses type 1 fimbriae was also adsorbed on the designed sensing surface with KADS(JM109) = 5.84 × 103 CFU/mL. It was illustrated that the novel electrochemical impedance biosensor could be more rapid and reliable for studying interactions between pathogen and glycan, and it was also perspective for a new point-of-care diagnostic tool for evaluating the pathogenicity bacteria.

A label-free electrochemical biosensor based on tubulin immobilized on gold nanoparticle/glassy carbon electrode for the determination of vinblastine.

Vinblastine (VLB) is prescribed for a wide variety of cancers. Therefore, development of sensitive methods for early diagnosis is urgently required. In this work, a highly sensitive and label-free impedimetric biosensor was fabricated for the electrochemical detection of VLB. First, the gold nanoparticles (AuNPs) were electrodeposited on the surface of a glassy carbon electrode (GCE). 3-Mercaptopropionic acid (MPA) was self-assembled over the AuNPs. Then, tubulin (TUB), as a receptor, was covalently immobilized atthe AuNPs/GCE surface via carbodiimide coupling reaction using N-(3 dimethylaminopropyl)-N'-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The step-by-step modification process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of a redox probe [Fe(CN)6]3-/4-. The VLB concentration was measured through the increase of impedance values in the corresponding specific binding of VLB and TUB. The increased electron-transfer resistance (R et) values were proportional to the value of VLB concentrations in the range of 0.4 to 65.0nmolL-1 with a detection limit of 8.4×10-2nmolL-1 (SN-1=3). The practical analytical performance of the proposed method was demonstrated by determination of VLB in plant extracts and human serum samples with satisfactory recoveries.

Nanomaterials in label-free impedimetric biosensor: Current process and future perspectives

Today, the application of nanomaterials has been gaining prominence in the field of biosensing technologies as it offers more and more impact studies to improve the sensitivity k]specificity k]speed of response and cost effectiveness k]Especially in electrochemical impedance spectroscopy technique k]an outstanding electrical biotransducer k]nanomaterials have been extensively used in almost all studies over the past decade k]The nanostructures used in the construction of sensing devices vary in size k]shape and physicochemical properties k]such as nanoparticles k]nanotubes k]nanosheets k]nanoelectrodes or nanochannels k]The use of nanomaterials in impedimetric biosensor involves two key principles: (1) to develop a new sensing substrate via surface modification techniques with the aim of increasing the impedimetric response and (2) to develop a compatible sensing platform to facilitate the detection based on the resemblance in size between targets and signal transducers k]Herein k]the review shows the recent trends of using engineered nanomaterials in impedimetric biosensors as a factor of signal amplification k]The detection events are diverse from biomolecular recognitions including enzymes k]proteins k]nucleic acids k]etc k]to whole cells monitoring k]Additionally k]the shortcomings of current techniques and future perspectives of impedimetric point-of-care devices are also included.

Assessment of analytical methods to determine pyrethroids content of bednets.

To present and evaluate simple, cost-effective tests to determine the amount of insecticide on treated materials. We developed and evaluated a competitive immunoassay on two different platforms: a label-free impedimetric biosensor (EIS biosensor) and a lateral flow. Both approaches were validated by gas chromatography (GC) and ELISA, gold standards for analytical methods and immunoassays, respectively. Finally, commercially available pyrethroid-treated ITN samples were analysed. Different extraction methods were evaluated. Insecticide extraction by direct infusion of the ITN samples with dichloromethane and dioxane showed recovery efficiencies around 100% for insecticide-coated bednets, and >70% for insecticide-incorporated bednets. These results were comparable to those obtained with standard sonication methods. The competitive immunoassay characterisation with ELISA presented a dynamic range between 12 nm and 1.5 μm (coefficient of variation (CV) below 5%), with an IC50 at 138 nm, and a limit of detection (LOD) of 3.2 nm. EIS biosensor had a linear range between 1.7 nm and 61 nm (CV around 14%), with an IC50 at 10.4 nm, and a LOD of 0.6 nm. Finally, the lateral flow approach showed a dynamic range between 150 nm and 1.5 μm, an IC50 at 505 nm and a LOD of 67 nm. ELISA can replace chromatography as an accurate laboratory technique to determine insecticide concentration in bednets. The lateral flow approach developed can be used to estimate ITN insecticide concentration in the field. This new technology, coupled to the new extraction methods, should provide reliable guidelines for ITN use and replacement in the field.

Porous graphene oxide nanostructure as an excellent scaffold for label-free electrochemical biosensor: Detection of cardiac troponin I

Herein, we report the fabrication of a novel label-free impedimetric biosensor employing porous graphene oxide (PrGO) nanostructures for the specific detection of cardiac troponin-I (cTnI) to establish the myocardial infarction (MI). This nano-immunosensor demonstrates an outstanding selectivity and high sensitivity towards the human-cTnI analyte. An excellent detection limit of 0.07ngmL−1 and dynamic linear range of 0.1–10ngmL−1 were calculated for anti-cTnI/PrGO/GC. Finally, this biosensor was employed to check the concentration of the MI biomarker in real clinical samples and the results are in good agreement with standard enzyme-linked fluorescence assay (ELFA) method.

Micro-flow Immunosensor Based on Thin-film Interdigitated Gold Array Microelectrodes for Cancer Biomarker Detection.

In this paper, we reported the development of a micro-flow label-free impedimetric biosensor based on the use of thin-film interdigitated gold array microelectrodes (IDA) for the detection of carbohydrate antigen 125 (CA125). The immunosensor is developed through the electropolymerization of anthranilic acid (AA) on the surface of IDA electrodes followed by the covalent attachment of anti-CA125 monoclonal antibody. CA125 protein affinity reaction was then evaluated by means of electrochemical impedance spectroscopy (EIS). The sensor was characterized by electrochemical techniques and scanning electron microscopy (SEM). Using the optimized experimental conditions, the developed immunosensor showed a good analytical performance for CA125 detection from 0 to 100 U/mL with estimated limit of detection (LOD = 3Sblank/Slope) of 7 U/mL.

Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample

Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of foodborne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs.We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen-printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1×101 to 1×108CFUmL−1, with a limit of quantification (LOQ) of 1×101CFUmL−1 and a limit of detection (LOD) of 6CFUmL−1. Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1×102, 1×104 and 1×106CFUmL−1) apple juice samples.