Health care and the medical industry, environmental monitoring and food sector are just a few examples of human’s major concerns. Design and analytical applications of (bio)sensors and sensing (nano)materials in these fields which have drawn tremendous attention by scientific community, require multidisciplinary knowledge in materials, transducers, and measurement methodologies. Among different types of transducers, electrochemical transducers have gained a lot of interest due to their simplicity, ease of fabrication and integration, selectivity, and sensitivity. Application of sensing materials, in particular nanomaterials, provide several improvements for analytical sensing such as selectivity, sensitivity, robustness, and fast response. Therefore, different nanomaterials due to their excellent characterization are exploited as key instruments for the design of high-performant analytical assays in various fields.

Considering this established nanomaterial-based electrochemical sensing applications as alternatives to conventional methods in various fields, in this thesis, we synthesized and characterized some (nano)materials such as gold nanostars (AuNSs), iron oxide/zinc oxide (α-Fe₂O₃/ZnO) nanocomposite for sensing applications in environmental monitoring. We fabricated screen printed Ruthenium (IV) oxide (RuO₂-Nf) pH electrodes and applied them for continuous pH monitoring in milk and during milk coagulation. Although the results indicated the applicability of the RuO₂-Nf electrodes for continuous pH measurement in milk as a replacement of traditional glass electrode, they are not suitable for more viscous samples. Later we investigated the cleaning procedure for these pH electrodes, and we showed that soaking them in the solution of 5% pepsin in 0.1 M HCl restores the electrodes to their initial state for pH measurement in food samples. In another work we developed a molecular imprinted polymer-based biosensor for successful detection of prostate-specific antigen. At the end we investigated the effect of pH on the growth of pathogenic bacteria using electrical impedance spectroscopy.

Screen-printed RuO2 pH electrodes are suitable for pH determination not only in water samples but also in different food matrixes, e.g., beverages, juices and milk. Nevertheless, the application of the screen-printed RuO2 electrodes in milk is impossible without covering the electrodes with a protective Nafion membrane that prevents the contamination of the pH-sensitive area of the electrode with sample residues. However, not much attention has been paid to the cleaning procedure of Nafion-covered screen-printed RuO2 electrodes (RuO2-Nf). In this paper, we show that cleaning the electrodes by soaking them in the solution of 5% pepsin in 0.1 M HCl allows restoring the electrode to its initial state for measuring pH in food samples.

Escherichia coli O157:H7 (E. coli O157:H7) is an enterohemorrhagic E. coli (EHEC), which has been issued as a major threat to public health worldwide due to fatal contamination of water and food. Thus, its rapid and accurate detection has tremendous importance in environmental monitoring and human health. In this regard, we report a simple and sensitive electrochemical DNA biosensor by targeting Z3276 as a genetic marker in river water. The surface of the designed gold electrode was functionalized with gold nanostars and an aminated specific sensing probe of E. coli O157:H7 to fabricate the genosensor. Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were applied for electrochemical characterization and detection. The synthesized gold nanostars were characterized using different characterization techniques. The fabricated DNA-based sensor exhibited a high selective ability for one, two, and three-base mismatched sequences. Regeneration, stability, selectivity, and kinetics of the bioassay were investigated. Under optimal conditions, the fabricated genosensor exhibited a linear response range of 10(-5) to 10(-17) mu M in the standard sample and 7.3 to 1 x 10(-17) mu M in water samples with a low limit of quantification of 0.01 zM in water samples. The detection strategy based on silver plated gold nanostars and DNA hybridization improved the sensitivity and specificity of the assay for E. coli O157:H7 detection in real water samples without filtration. The detection assay has the advantages of high selectivity, sensitivity, low amounts of reagents, short analysis time, commercialization, and potential application for the determination of other pathogenic bacteria.

Gold nanoparticles (AuNPs) are highly compelling nanomaterials for biomedical studies due to their unique optical properties. By leveraging the versatile optical properties of different gold nanostructures, the performance of biosensing and biomedical imaging can be dramatically improved in terms of their sensitivity, specificity, speed, contrast, resolution and penetration depth. Here we review recent advances of optical biosensing and bioimaging techniques based on three major optical properties of AuNPs: surface plasmon resonance, surface enhanced Raman scattering and luminescence. We summarize the fabrication methods and optical properties of different types of AuNPs, highlight the emerging applications of these AuNPs for novel optical biosensors and biomedical imaging innovations, and discuss the future trends of AuNP-based optical biosensors and bioimaging as well as the challenges of implementing these techniques in preclinical and clinical investigations.

Leishmaniasis considered as the most crucial epidemic-prone diseases according to the World Health Organization. Early diagnoses and therapy of Leishmania infection is a great challenge since, it has no symptom and is resistance to drugs. Therefore, there is an urgent need for sensitive and precise detection of this pathogen. In this study, a new method was developed for optical biosensing of Leishmania spp sequence based on hybridization of Citrate capped Ag nanoparticles bonded to specific single stranded DNA probe of Leishmania spp. Aggregation of the Citrate capped Ag nanoparticles in the existence or lack of a cDNA sequence of Leishmania, cause eye catching and considerable significant alter in the UV–vis. The obtained low limit of quantification (LLOQ) of was achieved as 1ZM. Based on experimental results in optimum conditions, quick bioanalysis of Leishmania spp sequence was performed (2 min). So, this probe can be used for the clinical diagnosis of this pathogen and infection disease. © 2020 The Author(s) Analytical chemistry; Nanotechnology, Nanostructure; Affinity binding; Leishmaniasis; Spectrophotometer; Spectrofluorimetric; Biosensing © 2020 The Author(s)

In this study, electrically-conducting poly [Toluidine Blue (PTB)] was applied as artificial receptor. It was organized by molecular imprinting approaches and via electrochemical technique for the sensitive monitoring of prostate-specific antigen (PSA). The protein-imprinted PTB was electropolymerized in a pre-formed glutaraldehyde-cysteamine (GA-Cys A) matrix on the surface of gold electrode, which significantly boosted the stability against degradation of the Molecular Imprinted Polymer (MIP) on the surface of pre-modified gold electrode. Moreover, the MIP bio-receptor ability towards protein recognition was explored by some electrochemical techniques. The binding affinity of MIP system was considerably upper than that of non-imprinted polymer (NIP) system, indicating the success of the method in generating imprinted materials that was specifically use to PSA protein. The incubation of the MIP modified electrode in various concentration of PSA (from 1-60 μg/L) resulted in the increase of the Fe (CN)₆^3-/4- redox peak current. The bio-device also showed linear response from 1-60 μg/L and LLOQ of 1 μg/L by using DPV technique, leading to PSA monitoring in clinical samples. The proposed MIP-based biosensor was satisfactorily applied to the determination of PSA in human plasma samples. Therefore, the developed bio-device provides a new approach for sensitive, simple, rapid, and cost-effective monitoring of 1 μg/L of PSA. Notably, this approach could appear as an appropriate candidate for point-of-care (POC) use in clinical and biomedical analyses.

Acinetobacter baumannii is the main cause of nosocomial infections in blood, urinary tract, wounds and in lungs leading to pneumonia. Apart from its strong predilection to be the cause of serious illnesses in intensive care units. Herein, we present a specific and sensitive approach for the monitoring of Acinetobacter baumannii genome based on citrate capped silver nanoparticles (Cit-AgNPs) using spectroscopic methods. In this study, (5' SH-TTG TGA ACT ATT TAC GTC AGC ATG C3') sequence was used as a probe DNA (pDNA) of Acinetobacter baumannii. Then, complementary DNA (cDNA) was used for hybridization. After the hybridization of pDNA with cDNA, target DNA (5' GCA TGC TGA CGT AAA TAGTTC ACA A 3') was recognized and detected using turn-on fluorescence bioassay. After the hybridization of pDNA with cDNA, the target DNA was successfully measured in optimum time of 2 min by spectrophotometric techniques. Moreover, the selectivity of designed bioassay was evaluated in the presence of two mismatch sequences and excellent differentiation was obtained. 1 Zepto-molar (zM) of low limit of quantification (LLOQ) was achieved by this genosensor. The present study paved the way for quick (2 min) and accurate detection of Acinetobacter baumannii, which can be a good alternative to the traditional methods. Current study proposed a novel and significant diagnostic test towards Acinetobacter baumannii detection based on silver nanoparticles aggregation which has the capability of being a good alternative to the traditional methods. Moreover, the proposed genosensor successfully could be applied for the detection of other pathogens.

Escherichia coliO157:H7 (E. coliO157:H7) is a pathogenic strain ofEscherichia coliwhich has issued as a public health threat because of fatal contamination of food and water. Therefore, accurate detection of pathogenicE. coliis important in environmental and food quality monitoring. In spite of their advantages and high acceptance, culture-based methods, enzyme-linked immunosorbent assays (ELISAs), polymerase chain reaction (PCR), flow cytometry, ATP bioluminescence, and solid-phase cytometry have various drawbacks, including being time-consuming, requiring trained technicians and/or specific equipment, and producing biological waste. Therefore, there is necessity for affordable, rapid, and simple approaches. Electrochemical biosensors have shown great promise for rapid food- and water-borne pathogen detection. Over the last decade, various attempts have been made to develop techniques for the rapid quantification ofE. coliO157:H7. This review covers the importance ofE. coliO157:H7 and recent progress (from 2015 to 2020) in the development of the sensitivity and selectivity of electrochemical sensors developed forE. coliO157:H7 using different nanomaterials, labels, and electrochemical transducers.