An electrochemical immunosensor based on agarose hydrogel films for rapid determination of ractopamine

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

A cloth-based electrochemiluminescence sensor for determination of salbutamol residues in pork samples

The fabrication of a cloth-based analytical device combined with electrochemiluminescence detection was established for the rapid determination of salbutamol in pork samples. A hand-coloring method to pattern the hydrophobic chamber was employed, and a three-carbon electrode system was subsequently screen printed onto the patterned cotton chamber. Further modifications of the working electrode surface were conducted using platinum nanoparticles and chitosan solution. The salbutamol enhanced the electrochemiluminescence signal of tris(2,2'-bipyridyl)ruthenium(II) complex in the Britton-Robinson buffer of pH 9.5 and the potential quantitative assay for SAL detection was exhibited. The proposed sensor illustrated a linear calibration curve of the logarithmic SAL concentration in the range of 5 × 10^-2 to 5 × 10⁴ µg L^-1 (r² > 0.996). A limit of detection of 6.8 ng L^-1 was observed. The CAD-ECL sensor was successfully applied for the determination of salbutamol residuals in pork samples. The method validation was performed using the LC-MS method.

Hydrogel Nanoarchitectonics: An Evolving Paradigm for Ultrasensitive Biosensing

The integration of nanoarchitectonics and hydrogel into conventional biosensing platforms offers the opportunities to design physically and chemically controlled and optimized soft structures with superior biocompatibility, better immobilization of biomolecules, and specific and sensitive biosensor design. The physical and chemical properties of 3D hydrogel structures can be modified by integrating with nanostructures. Such modifications can enhance their responsiveness to mechanical, optical, thermal, magnetic, and electric stimuli, which in turn can enhance the practicality of biosensors in clinical settings. This review describes the synthesis and kinetics of gel networks and exploitation of nanostructure-integrated hydrogels in biosensing. With an emphasis on different integration strategies of hydrogel with nanostructures, this review highlights the importance of hydrogel nanostructures as one of the most favorable candidates for developing ultrasensitive biosensors. Moreover, hydrogel nanoarchitectonics are also portrayed as a promising candidate for fabricating next-generation robust biosensors.

A flexible paper based electrochemical portable biosensor towards recognition of ractopamine as animal feed additive: Low cost diagnostic tool towards food analysis using aptasensor technology

Due to the costly and time-consuming traditional techniques, providing a low-cost, portability and flexibility diagnostic tool with the ability to monitor and detect various animal feed additive is highly demanded. Over the years, paper-based biosensors have emerged as point of care (POC) diagnostic, easy-to-use and miniaturized tools. However, they have been suffered from low sensitivity. Aptamer as appropriate bioreceptor can overcome the most common disadvantage of paper based sensor by increasing selectivity and sensitivity. In this study, a novel paper-based electrochemical aptasensor was successfully developed to detection of ractopamine (RAC). RAC concentration was evaluated using a designed three-electrode paper based biodevice system. Under the optimal experimental conditions, the engineered aptasensor provided good sensitivity and selectivity for the detection of RAC. Using proposed flexible sensor RAC was determined in the range of 0.001 µM to 100 mM which the lower limit of quantitation (LLOQ) was obtained as 0.01 µM. Finally, aptasensor was used to the monitoring of RAC in untreated human plasma specimens which LLOQ and linear range were 0.01 µM and 0.01 µM to 10 mM, respectively. We hope that the exploitation of aptamer in electrochemical paper based sensor will be able to broaden our understanding for developing the application of low-cost and portable biodevices for the sensitive and selective paper-based sensor to identify other chemical and biological compounds.

d-Penicillamine functionalized dendritic fibrous nanosilica (DFNS-DPA): synthesise and its application as an innovative advanced nanomaterial towards sensitive quantification of ractopamine

During the twentieth century, ractopamine (RAC) as one of the important and frequently used feed additives and doping agents has attracted considerable attention in the animal breeding industry and sports competitions.

Fabrication of an electrochemical biodevice for ractopamine detection under a strategy of a double recognition of the aptamer/molecular imprinting polymer

The importance of RAC tracking in human biofluids has boosted many demands for designing an ultrasensitive tool to determine the trace value of the RAC from clinical, judicial, and forensic centers. In this study, an electrochemical biodevice has developed for the highly selective detection of this illegal feed additive under a double recognition strategy of the aptamer (Apt) and molecular imprinting polymer (MIP) on a glassy carbon electrode (GCE). The sensing relies on this fact that both the MIP and Apt act synergistically to trap the RAC molecules. The sensing surface fabrication steps have been monitored by some electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV(. The charge transfer resistance (R_ct) value of the redox probe as a representative of the biodevice response has increased linearly with the RAC concentration increasing in a dynamic range of 1 fM to 1.90 µM. The detection limit (LOD) value has been estimated to be 330 aM, lower than all of the reported methods in the RAC sensing. Furthermore, the practical feasibility of biodevice has been evaluated in some human blood serum and urine samples. This strategy offers some useful advantages in reliable detection of the RAC, which may help in the routine analysis, as mandated by regulatory agencies.

Two-dimensional binary nanosheets (Bi2Te3@g-C3N4): Application toward the electrochemical detection of food toxic chemical

Bismuth telluride is considered as an efficient and super-active electrocatalyst in the sector of electrochemical application. Herein, we prepared binary nanosheets (Bi₂Te₃) through simple solvothermal and hydrothermal method. Furthermore, to enhance the electrocatalytic activity, graphitic carbon nitrides nanosheets (g-C₃N₄) were used to prepare the composition of Bi₂Te₃/g-C₃N₄ binary nanosheets (BNs) with help of hydrothermal energy. Moreover, Bi₂Te₃/g-C₃N₄ hybrid was characterized by various techniques (XRD, XPS, SEM, TEM, EDS and EIS analysis). The electrochemical performance of Bi₂Te₃/g-C₃N₄ BNs modified GCEs were analyzed by electrochemical technique (DPV, EIS and CV methods). As modified the Bi₂Te₃/g-C₃N₄ BNs modified electrode exhibits excellent electrochemical activity towards food toxic ractopamine (RAC) with high-sensitive and nano-molar detection limit (LOD). Besides, the practical ability was analyzed to detect the RAC in meat samples using Bi₂Te₃/g-C₃N₄ BNs modified GCE.

Advancements in Hydrogel-Functionalized Immunosensing Platforms

Explicit antigen-antibody binding has accelerated the development of immunosensors for the detection of various analytes in biomedical and environmental domains. Being a subclass of biosensors, immunosensors have been a significant area of research in attaining high sensitivity and an ultralow sensing limit to detect biological analytes present in trace levels. The highly porous structure, large surface area, and excellent biocompatibility of hydrogels enabling the retainability of the activity and innate framework of the attached biomolecules make them a suitable candidate for immunosensor fabrication. Hydrogels based on polycarboxylate, cellulose, polyaniline, polypyrrole, sodium alginate, chitosan, and agarose are exploited in conjunction with other nanomaterials such as AuNPs, GO, and MWCNTs to augment the electron transfer during the immunosensing mechanism. Surface plasmon resonance, electrochemiluminescence, colorimetric, and electrochemical assays are different strategies utilized for the signal transduction in hydrogel-based immunosensors during the formation of the antigen-antibody complex. These hydrogel-based immunosensors exhibit rapid response, excellent stability, reproducibility, high selectivity and high sensitivity, a broad range of detection, an ultralow limit of detection, and display results similar to those for the ELISA test. This review propounds different hydrogel-functionalized immunosensing platforms classified on the basis of their signal transduction for the detection of disparate cancer biomarkers (tumor necrosis factor, α-fetoprotein, prostate-specific antigen, carbohydrate antigen 24-2, carcinoembryonic antigen, neuron-specific enolase, and cytokeratin antigen 21-1), hormones (cortisol, cortisone, and human chorionic gonadotropin), human IgG, and ractopamine in animal feeds.

Platinized agarose microspheres as a new modifier in graphite paste electrodes for the electrochemical determination of 4-aminophenol

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant. In this study, platinized agarose microspheres (PtAM) were used for the first time, for the preparation of a novel, modified graphite paste electrode (GPE/PtAM) for the electrochemical determination of 4-AP. PtAM was characterized using transmission electron microscopy, field emission scanning electron microscopy and energy dispersive X-ray analysis. The electrochemical response characteristics of GPE/PtAM towards 4-AP were investigated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The value of the charge transfer resistance obtained for GPE/PtAM was 27.3 Ω. Microscopic surface areas and the surface concentration of the electroactive species for GPE/PtAM were calculated to be 0.077 cm² and 1.13 × 10⁻³ mol cm⁻², respectively. The electron transfer coefficient, diffusion coefficient and standard heterogeneous rate constants of 4-AP were calculated as 0.274, 4.56 × 10⁻⁴ cm² s⁻¹, and 3.32 × 10⁻¹ cm s⁻¹, respectively. The influence of pH on the oxidation of 4-AP was investigated and a pH value of 2.0 (using a phosphate buffer solution) was selected as the optimum pH. Under optimum conditions, the calibration was linear between 0.8 and 87 μM with a detection limit of 45 nM. Moreover, GPE/PtAM was applied to determine the concentrations of 4-AP in water samples with satisfactory results.

In the environment, 4-aminophenol (4-AP) is present as a highly toxic compound and water pollutant.

AgNPs/QDs@GQDs nanocomposites developed as an ultrasensitive impedimetric aptasensor for ractopamine detection

Developing easy-to-use and miniaturized sensors for in-field monitoring of targets which is related to human health is necessary. Ractopamine (RAC) is a feed additive with serious side effects that is forbidden in many countries. This study reports the fabrication of an impedimetric aptasensor for ultrasensitive and selective detection of the RAC in human biological fluids. Accordingly, an efficient nanocomposites was synthesized by a beneficial combination of graphene quantum dots (GQDs), quantum dots (QDs) and silver nanoparticles (AgNPs) for modifying a glassy carbon electrode (GCE). This nanocomposite is promising to present a synergistic effect in the increase of the active surface area of the modified electrode to more load the biocapture of the target. Next, the RAC-binding aptamer (Apt) was attached to the AgNPs/QDs@GQDs/GCE surface and a sensitive layer for the RAC detection was embedded. A RAC-Apt complex was formed upon adding the RAC and the changes of the electrochemical behavior were studied by some electrochemical techniques such as electrochemical impedance spectroscopy (EIS). Under optimal conditions, the charge transfer resistance (R_ct) value was increased linearly with increasing of the RAC concentrations in the range of 1 fM to 901.4 nM. Limit of detection (LOD) was calculated to be 330 aM which is superior by other reported electrochemical methods in the RAC sensing. The applicability of the aptasensor was tested in human urine and blood serum as the real samples and satisfactory results of specificity were achieved. It seems that the proposed strategy not only provides a new ultrasensitive strategy for RAC detection but also expands the application of the sensing interface to develop other aptasensors by changing the Apt sequence.

Sonochemical synthesis of perovskite-type barium titanate nanoparticles decorated on reduced graphene oxide nanosheets as an effective electrode material for the rapid determination of ractopamine in meat samples

A simple and facile ultrasound based sonochemical method to incorporate Perovskite-type barium titanate (BaTiO₃) nanoparticles inside the layered and reduced graphene oxide sheets (rGOs) is reported. BaTiO₃@rGOs nanocomposite was characterized by FESEM, HRTEM, EDX, mapping, XRD, XPS and EIS. The results show that the decoration and also incorporation of BaTiO₃ nanoparticles in the multi-layered and ultrasound reduced graphene oxide matrix. Non-enzymatic and differential pulse voltammetric sensor of ractopamine (food toxic) based on the BaTiO₃@rGOs nanocomposite modified screen printed carbon electrode is developed. Compared with the original BaTiO₃/SPCE and rGOs/SPCE, the BaTiO₃@rGOs/SPCE displays excellent current response towards ractopamine and gives linearity in the range of 0.01-527.19 µM ractopamine in neutral phosphate buffer (pH 7.0). The BaTiO₃@rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared BaTiO₃ NPs@rGOs/SPCE has been applied to the determination of ractopamine in pork and chicken samples.

Increasing the potential of cell-penetrating peptides for cancer therapy using a new pentagonal scaffold

Cancer treatment is one of the major fields of interest for the scientific community. Investment in cancer research is costly but essential to provide patients with more effective and safe treatments. In this project, we describe the synthesis and characterization of new thiazole derivatives coupled to CPP2, a cell-penetrating peptide (CPP) reported for colon cancer cells. Using a human adenocarcinoma-derived cell line (Caco-2), these new CPPs were evaluated for antiproliferative (³H-thymidine incorporation) and cytotoxic effect (extracellular lactate dehydrogenase activity). One of these derivatives, the BTZCA thiazole compound and its peptide-conjugated (BTZCA-CPP2) also showed the ability to decrease tumour cell viability and proliferation, with potential cytotoxic effect against human breast cancer MCF-7 cells. Then, cytotoxicity studies were developed against J774, L929 and THP1 cell lines and this new family showed no significant cytotoxicity, when compared to their counterparts alone (BTZCA and CPP2). The use of smaller CPP conjugated with this family of derivatives can be also considered in future for the development of new drugs to cancer therapy.

Novel ractopamine-protein carrier conjugation and its application to the lateral flow strip test for ractopamine detection in animal feed

In this work, a novel conjugate of ractopamine and bovine serum albumin (RAC-BSA) has been developed via the Mannich reaction, with a mole coupling ratio for RAC-BSA of 9:1. The proposed conjugation method provides a simple and one-step method with the use of fewer reagents compared with other conjugation methods for competitive immunoassays. RAC-BSA conjugation was used to fabricate a competitive lateral flow strip test for RAC detection in animal feed. For sample preparation, RAC was spiked in swine feed purchased from the local markets in Thailand, and methanol and running buffer at a volume ratio of 10:90 was used as extraction buffer. The procedures for sample preparation were completed within 25 min. Under optimal conditions, the limit of detection (LOD), assessed by the naked eye within 5 min, was found to be 1 ng/g. A semi-quantitative analysis was also conducted using a smart phone and computer software, with a linearity of 0.075-0.750 ng/g, calculated LOD of 0.10 ng/g, calculated limit of quantitation of 0.33 ng/g, and good correlation of 0.992. The recoveries were found in the range of 96.4%-103.7% with a relative standard deviation of 2.5%-3.6% for intra- and inter-assays. Comparison of the results obtained by the strip test with those obtained by enzyme-linked immunosorbent assay had a good agreement in terms of accuracy. Furthermore, this strip test exhibited highly specific RAC detection without cross reactivity with related compounds. Therefore, the RAC-BSA conjugation via the Mannich reaction can be accepted as a one-step and easy conjugation method and applied to the competitive lateral flow strip test.

Cross-linked chitosan/thiolated graphene quantum dots as a biocompatible polysaccharide towards aptamer immobilization

Chitosan has a number of commercial and possible biomedical uses. Chitosan as a polysaccharide is a bioactive polymer with a variety of applications due to its functional properties such as antibacterial activity, non-toxicity, ease of modification, and biodegradability. In this work, cross-linked chitosan/thiolated graphene quantum dot as a biocompatible polysaccharide was modified by gold nanoparticle and used for immobilization of ractopamine (RAC) aptamer. A highly specific DNA-aptamer (5'-SH-AAAAAGTGCGGGC-3'), selected to RAC was immobilized onto thiolated graphene quantum dots (GQDs)-chitosan (CS) nanocomposite modified by gold nanostructures (Au NSs) and used for quantification of RAC. Different shapes of gold nanostructures with various sizes from zero-dimensional nanoparticles to spherical structures were prepared by one-step template-assistant green electrodeposition method. Fully electrochemical methodology was used to prepare a new transducer on a glassy carbon surface which provided a high surface area to immobilize a high amount of the aptamer. Therefore, a label free electrochemical (EC) apta-assay for ultrasensitive detection of RAC was developed. A special immobilization media consisting of Au NSs/GQDs-CS/Cysteamine (CysA) was utilized to improve conductivity and performance of the biosensor. The RAC aptamer was attached on the Au NSs of the composite membrane via AuS bond. The fabrication process of the EC aptamer based assay was characterized by some electrochemical techniques. The peak currents obtained by differential pulse voltammetry decreased linearly with the increasing of RAC concentrations and the apta-assay responds approximately over a wide dynamic range of RAC concentration from 0.0044 fM to 19.55 μM. The low limit of quantification was 0.0044 fM.

Integrated Affinity Biosensing Platforms on Screen-Printed Electrodes Electrografted with Diazonium Salts

Adequate selection of the electrode surface and the strategies for its modification to enable subsequent immobilization of biomolecules and/or nanomaterials integration play a major role in the performance of electrochemical affinity biosensors. Because of the simplicity, rapidity and versatility, electrografting using diazonium salt reduction is among the most currently used functionalization methods to provide the attachment of an organic layer to a conductive substrate. This particular chemistry has demonstrated to be a powerful tool to covalently immobilize in a stable and reproducible way a wide range of biomolecules or nanomaterials onto different electrode surfaces. Considering the great progress and interesting features arisen in the last years, this paper outlines the potential of diazonium chemistry to prepare single or multianalyte electrochemical affinity biosensors on screen-printed electrodes (SPEs) and points out the existing challenges and future directions in this field.

Rapid screening of toxic salbutamol, ractopamine, and clenbuterol in pork sample by high-performance liquid chromatography—UV method

A rapid and simple high-performance liquid chromatography–UV method was developed for the separation and quantification of salbutamol, ractopamine, and clenbuterol in pork. A mixture of acetonitrile–formic acid–ammonium acetate was used as the mobile phase to separate three β-agonists on a C18 column with gradient. The effects of the addition of formic acid and ammonium acetate to mobile phases on the separation of β-agonists were investigated. These additives can greatly improve the resolution and sensitivity. Under the optimized chromatographic condition, this separation does not need extra sample preparation. Complete baseline separation of three β-agonists was achieved in < 20 minutes; the linear range is 0.2–50 μg/L with a correlation coefficient R² value of > 0.99. Excellent method reproducibility was found by intra- and interday precisions with a relative standard deviation of < 3%. The detection limit (S/N = 3) was found to be <0.05 μg/L; this method can be used for routine screening of the β-agonist residues in foods of animal origin before being identified by confirmatory methods.

A Novel Electrochemical Sensor for the Analysis of Salbutamol in Pork Samples by Using NiFe2O4 Nanoparticles Modified Glassy Carbon Electrode

In this work, a simple and sensitive electrochemical method sensor was developed to determine salbutamol based on magnetic NiFe2O4nanoparticles modified glassy carbon electrode. It was found the anodic peak current of salbutamol was linear with the concentration of salbutamol from 2.0 μM to 60 μM with a detection limit of 1.0 μM (S/N=3). The developed method was successfully applied to determine salbutamol content in pork samples with satisfactory results.

Multi-spectroscopic methods combined with molecular modeling dissect the interaction mechanisms of ractopamine and calf thymus DNA

The toxic interaction of ractopamine (RAC) with calf thymus DNA (ct DNA) was studied in vitro using multi-spectroscopic methods and molecular modeling methods. The hypochromic effect without a noticeable shift in UV-vis absorption indicated that the minor groove binding mode existed in the interaction between RAC and DNA. The fluorescence quenching of RAC was observed with the increasing addition of DNA and was proved to be the static quenching. The binding constant and the binding site sizes were 4.13 × 10(3) and 0.97, respectively. The thermodynamic calculation demonstrated that the hydrogen bond and van der Waals were main acting forces. This result further confirmed the existence of groove binding mode. Afterwards, we found another interaction mode, electrostatic binding mode through the fluorescence polarization, ionic effects and denatured DNA experiments. Circular dichroism spectroscopy (CD) was then employed to monitor the conformation changes of DNA. Molecular modeling studies illustrated the visual display of the binding mode and the detailed information of the H-bond.

A signal-on electrochemiluminescence aptamer biosensor for the detection of ultratrace thrombin based on junction-probe

A novel signal-on junction-probe electrogenerated chemiluminescence (ECL) aptamer biosensor has been developed for the detection of ultratrace thrombin based on a structure-switching ECL-quenching mechanism. The ECL aptamer biosensor comprises two main parts: an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and ruthenium (II) tris-bipyridine (Ru(bpy)(3)(2+)-AuNPs) on the surface of gold electrode (GE), and the ECL intensity switch contains three probes designed according to the "junction-probe" strategy. The first probe is capture probe (Cp) which was functionalized with a thiol group at one end and covalently attached to Ru(bpy)(3)(2+)-AuNPs modified GE through S-Au bonding. The second probe is aptamer probe (Ap), which containing 15-base anti-thrombin DNA aptamer. The third one is ferrocene-labeled probe (Fp), which was functionalized with ferrocene tag at one end. We demonstrated that, in the absence of thrombin, Cp, Ap and Fp will hybridize to form a ternary "Y" junction structure and resulted in a quenching of ECL of Ru(bpy)(3)(2+). Whereas, in the presence of thrombin, the Ap prefers to form the G-quadruplex aptamer-thrombin complex and lead to an obvious recovery of ECL of Ru(bpy)(3)(2+), which provided a sensing platform for the detection of thrombin. Using this reusable sensing platform, a simple, rapid and selective signal-on ECL aptamer biosensor for the detection of thrombin with a detection limit of 8.0×10(-15) M has been developed. The success in the present biosensor served as a significant step towards the development of monitoring ultratrace thrombin in clinical detection.

Electrochemiluminescent aptamer biosensor for the determination of ochratoxin A at a gold-nanoparticles-modified gold electrode using N-(aminobutyl)-N-ethylisoluminol as a luminescent label

A highly selective electrochemiluminescent biosensor for the detection of target nephrotoxic toxin, ochratoxin A (OTA), was developed using a DNA aptamer as the recognition element and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) as the signal-producing compound. The electrochemiluminescent aptamer biosensor was fabricated by immobilizing aptamer complementary DNA 1 sequence onto the surface of a gold-nanoparticle (AuNP)-modified gold electrode. ABEI-labeled aptamer DNA 2 sequence hybridized to DNA 1 and was utilized as an electrochemiluminescent probe. A decreased electrochemiluminescence (ECL) signal was generated upon aptamer recognition of the target OTA, which induced the dissociation of DNA 2 (ABEI-labeled aptamer electrochemiluminescent probe) from DNA 1 and moved it far away from the electrode surface. Under the optimal conditions, the decreased ECL intensity was proportional to an OTA concentration ranging from 0.02 to 3.0 ng mL(-1), with a detection limit of 0.007 ng mL(-1). The relative standard deviation was 3.8% at 0.2 ng mL(-1) (n = 7). The proposed method has been applied to measure OTA in naturally contaminated wheat samples and validated by an official method. This work demonstrates the combination of a highly binding aptamer with a highly sensitive ECL technique to design an electrochemiluminescent biosensor, which is a very promising approach for the determination of small-molecule toxins.

Square wave voltammetry versus electrochemical impedance spectroscopy as a rapid detection technique at electrochemical immunosensors

Square wave voltammetry (SWV) was compared to electrochemical impedance spectroscopy (EIS) in developing a label-free electrochemical immunosensor for the hormone estradiol. The immunosensor consists of a Au electrode anchored with a Au nanoparticle|thiolated Protein G-scaffold to facilitate immobilisation of an enhanced quantity of an almost uprightly aligned anti-estradiol capture antibody. Competitive immunoassays between an estradiol-bovine saline albumin complex and free estradiol in a sample were then promoted at the immunosensor. Next, SWV and EIS of [Fe(CN)(6)](3-/4-) were sequentially conducted at the immunosensor. SWV yielded familiar peak-shaped voltammograms with the peak currents readily employable in establishing calibration. A dynamic range up to approximately 1200 pg mL(-1) and a detection limit of 18 pg mL(-1) estradiol were achieved. In EIS, an electron transfer resistance estimated from the Nyquist plots was used in the calibration experiments. A comparable dynamic range up to approximately 1000 pg mL(-1) and a detection limit of 26 pg mL(-1) estradiol were obtained. However, a significantly 10 times longer analysis time and substantial effort were required to complete the EIS determinations relative to SWV. Moreover, a large amount of EIS data involving phase angle was collected but ignored because they would not contribute any useful information to quantitative determination. Overall, SWV was determined to be a more rapid, efficient, effective and low cost detection technique than EIS at label-free electrochemical immunosensors.