Electrochemical immunosensor for Enterobacter sakazakii detection based on electrochemically reduced graphene oxide–gold nanoparticle/ionic liquid modified electrode

Voltammetric determination of doxycycline in feedstock using modified carbon screen-printed electrode

In this work, we describe the development of an electrochemical sensing platform that employs electrochemically reduced graphene oxide (ErGO) and gold (Au) deposited on a screen-printed carbon electrode (SPCE) to synthesize Au/ErGO/SPCE for the determination of the antibiotic drug doxycycline (DC). A modified Hummer's approach was adopted to initially prepare graphene oxide, which was then characterized by using powder XRD, FTIR, and UV spectroscopy before being utilized for modification on SPCE. Cyclic voltammetry was performed to form ErGO on SPCE to give ErGO/SPCE followed by electrodeposition of gold to get a final modified electrode Au/ErGO/SPCE. The effect of experimental conditions, like scan rate and pH on the electrochemical behavior of DC for Au/ErGO/SPCE, was evaluated. Square wave voltammetry (SWV) and cyclic voltammetry (CV) measurements were used to assess the electro-oxidation of DC on Au/ErGO/SPCE, and the electrochemical reaction conditions were also optimized. Furthermore, Au/ErGO/SPCE-based electrochemical sensors showed good recovery and high accuracy for DC determination in the complex food matrix and blood serum. The limit of detection (LOD), the limit of quantification (LOQ), and the linear calibration range of DC on Au/ErGO/SPCE under optimum experimental conditions were 0.124 µm, 0.415 µm, and 1-100 µm respectively, with high sensitivity of 0.194 μA μM-1 cm-2. Finally, the proposed electrochemical sensing platform was effectively used to determine low DC concentrations in real samples such as chicken flesh and blood serum, indicating its wide range of applications in quality control.

Sandwich capture ultrasensitive sensor based on biohybrid interface for the detection of Cronobacter sakazakii

A simple, rapid and ultrasensitive visual sensing method for the detection of Cronobacter sakazakii (C. sakazakii) based on a biohybrid interface was established. During the entire sensing process, quadruple-cascade amplification showed its superior sensing performance. First, the prepared immunomagnetic beads (IMB) were used to isolate and enrich specific targets from the food matrix. After adding the fusion aptamer, the aptamer sequence specifically recognized the target and formed the immune sandwich structure of antibody-target-fusion aptamer. In addition, the fusion aptamer also included the template sequence of exponential amplification reaction (EXPAR), which contained the antisense sequence of the G-rich sequence. Therefore, a large number of G-rich sequences can be generated after EXPAR can be triggered in the presence of Bst. DNA polymerase, nicking endonuclease, cDNA, and dNTP. They were self-assembled into G-quadruplex structures and then combined with hemin to form G4/hemin DNAzyme, resulting in visible coloration and measuring absorbance at 450 nm for quantitative detection. The assay showed a limit of detection (LOD) of 2 CFU/mL in pure culture and 12 CFU/g in milk powder in optimal conditions. This method provides a promising strategy for rapid and point-of-care testing (POCT) since it does not require DNA extraction, medium culturing, and expensive instrumentation. KEY POINTS: •Single-cell level detection of C. sakazakii with ultrasensitive and rapidness •The fusion aptamer integrated recognition and amplification •Sensing analysis of C. sakazakii based on cascade amplification of biohybrid interface.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

Plasmonic ELISA based on DNA-directed gold nanoparticle growth for Cronobacter detection in powdered infant formula samples

The traditional gold nanoparticle (AuNP) growth-based plasmonic ELISA (pELISA) strictly and directly controlled by reducing reagents can achieve high sensitivity, but it remains fragile toward the surrounding environment. This work developed a sandwich pELISA for Cronobacter detection in powdered infant formula samples by mediating AuNP growth through DNA. In this assay, DNA adsorbed on the surface of gold nanoseeds guided the anisotropic crystal growth with hydroxylamine as a reducing reagent, and the catalase-hydrogen peroxide (Cat-H₂O₂) system was introduced to bridge the DNA-directed AuNP growth and pELISA, as such DNA can be cleaved into fragments by the hydroxyl radical generated from oxidation of H₂O₂ through Fenton reagents. Under optimized conditions, the proposed pELISA can qualitatively detect Cronobacter species (Cronobacter muytjensii ATCC 51329) by the naked eye with a cut-off limit of 3 × 10⁵ cfu/mL. This method also revealed a good linear range (3 × 10² to 3 × 10⁷ cfu/mL) for quantitative detection of C. muytjensii ATCC 51329 with a limit of detection of 1.6 × 10² cfu/mL, which is approximately 162.5 times lower than that of horseradish peroxidase-based conventional ELISA (2.6 × 10⁴ cfu/mL). By taking advantage of highly stable DNA-directed AuNP growth, the proposed method shows a good performance in powdered infant formula samples spiked with different concentrations of C. muytjensii ATCC 51329 with average recoveries ranging from 90.79 to 119.09% and coefficient of variation ranging from 4.24 to 9.55%. These values corresponded to an acceptable accuracy and precision for the proposed method. In brief, this work shows potential for screening other analytes in food safety, clinical diagnostics, and environmental monitoring.

Advances in electrochemical immunosensors

Immunosensors are compact tools on which antibody and antigen interactions are formed. The specific interaction between antibody and antigen is detected by using a transducer and an electrical signal is measured. This specific interaction between these molecules makes immunosensor very attractive for several applications in different fields. Electrochemical immunosensors are successful devices in selective and sensitive detection of several analytes. Electrochemical transducing methods such as voltammetric, potentiometric, conductometric or impedimetric have been utilized in different applications due to their excellent properties such as being low-cost, sensitivity and simplicity. In this chapter, the fundamentals of electrochemical immunosensors are summarized and different applications in food, environmental and clinical analyses are investigated and discussed.

A non-enzymatic electrochemical immunoassay for quantitative detection of Escherichia coli O157:H7 using Au@Pt and graphene

Herein, a non-enzymatic sandwich-type electrochemical immunoassay was fabricated for quantitative monitoring of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated Fe₃O₄ magnetic nanoparticles (Fe₃O₄@SiO₂) were modified with mouse anti-E. coli O157:H7 monoclonal antibody (Ab₁) to act as capture probes to reduce detection time and increase the sensitivity of the immunoassay. The Au@Pt nanoparticles were loaded on neutral red (NR) functionalized graphene to form composite complex rGO-NR-Au@Pt. rGO-NR-Au@Pt has high specific surface area and good biocompatibility. rGO-NR-Au@Pt was used as the carriers of detection antibodies (Ab₂). Au@Pt catalyzed the reduction of hydrogen peroxide (H₂O₂) to detection of E. coli O157:H7 with the thionine (TH) as electron mediator to effectually amply the current signal. Under the optimized conditions, a linear relationship between the reduction peak current change (ΔI_pc) and the logarithm of the E. coli O157:H7 concentration is obtained in the range from 4.0 × 10³ to 4.0 × 10⁸ CFU mL^-1 and the limit of detection (LOD) is 4.5 × 10² CFU mL^-1 at a signal-to-noise ratio of 3. The immunoassay exhibits acceptable specificity, reproducibility and stability on the detection of E. coli O157:H7. Furthermore, the immunoassay showed good performance in pork and milk samples. The results suggest that this immunoassay will be promising in the food safety area.

Detection of Antibiotics and Evaluation of Antibacterial Activity with Screen-Printed Electrodes

This review provides a brief overview of the fabrication and properties of screen-printed electrodes and details the different opportunities to apply them for the detection of antibiotics, detection of bacteria and antibiotic susceptibility. Among the alternative approaches to costly chromatographic or ELISA methods for antibiotics detection and to lengthy culture methods for bacteria detection, electrochemical biosensors based on screen-printed electrodes present some distinctive advantages. Chemical and (bio)sensors for the detection of antibiotics and assays coupling detection with screen-printed electrodes with immunomagnetic separation are described. With regards to detection of bacteria, the emphasis is placed on applications targeting viable bacterial cells. While the electrochemical sensors and biosensors face many challenges before replacing standard analysis methods, the potential of screen-printed electrodes is increasingly exploited and more applications are anticipated to advance towards commercial analytical tools.

Voltammetric sandwich immunoassay for Cronobacter sakazakii using a screen-printed carbon electrode modified with horseradish peroxidase, reduced graphene oxide, thionine and gold nanoparticles

The authors describe a sandwich-type of electrochemical immunoassay for rapid determination of the foodborne pathogen Cronobacter sakazakii (C. sakazakii). Polyclonal antibody against C. sakazakii (anti-C. sakazakii) and horseradish peroxidase were immobilized on a nanocomposite consisting of reduced graphene oxide, thionine and gold nanoparticles (AuNPs) that was placed on a screen-printed carbon electrode (SPCE). Thionine acts as an electron mediator which also shortens the electron transfer pathway from the conjugated HRP to the electrode surface and amplifies the electrochemical signal. The AuNPs, in turn, improve the electron transfer rate and increase the surface area for capturing antibody. The morphologies of the electrodes were characterized by means of field emission scanning electron microscopy. The electrochemical performance of the immunoassay was evaluated by cyclic voltammetry and differential pulse voltammetry. Under optimal experimental conditions, the electrochemical immunoassay, best operated at a woking potential of -0.18 V (vs. Ag/AgCl) and scan rate of 20 mV/s has a linear response that covers the 8.8 × 10⁴ to 8.8 × 10⁸ CFU·mL^-1 C. sakazakii concentration range, with a 1.0 × 10⁴ CFU·mL^-1 detection limit (at an S/N ratio of 3). The assay was applied to the detemination of C. sakazakii in spiked infant milk powder and gave recoveries ranging from 92.0 to 105.7%. Graphical abstract A sandwich-type electrochemical immunosensor was designed for C. sakazakii based on the use of rGO. TH, HRP, antibody and AuNPs were anchored on rGO. The nanocomposites were used as traces tag and H₂O₂ as enzyme substrates. AuNPs were modified on SPCE by electrodeposition.