Signal amplification for DNA detection based on the HRP-functionalized Fe3O4 nanoparticles

Chemical binding of horseradish peroxidase enzyme with poly beta-cyclodextrin and its application as molecularly imprinted polymer for the monitoring of H2 O2 in human plasma samples

In this study, a selective and sensitive molecular imprinting-based electrochemical sensors, for horseradish peroxidase (HRP) entrapment was fabricated using electro polymerization of ß-Cyclodextrin (ß-CD) on the surface of glassy carbon electrode. Poly beta-cyclodextrin P(ß-CD) provide efficient surface area for self-immobilization of HRP as well as improve imprinting efficiency. The proposed imprinted biosensor successfully utilized for detection of HRP with excellent analytical results which linear range is 0.1 mg/mL to 10 ng/mL with LOD of 2.23 ng/mL. Furthermore, electrocatalytical activity of the prepared biosensor toward the reduction of hydrogen peroxide was investigated in the ranges of 1 to 15 μM with a detection limit of 0.4 μM by using chronoamperometry technique. The developed biosensor was used for the detection of hydrogen peroxide in unprocessed human plasma sample.

Paper-based point-of-care test with xeno nucleic acid probes

Bridging the unmet need of efficient point-of-care testing (POCT) in biomedical engineering research and practice with the emerging development in artificial synthetic xeno nucleic acids (XNAs), this review summarized the recent development in paper-based POCT using XNAs as sensing probes. Alongside the signal transducing mode and immobilization methods of XNA probes, a detailed evaluation of probe performance was disclosed. With these new aspects, both researchers in synthetic chemistry / biomedical engineering and physicians in clinical practice could gain new insights in designing, manufacturing and choosing suitable reagents and techniques for POCT.

Ultrasensitive Electrochemical Biosensor of Bacterial 16S rRNA Gene Based on polyA DNA Probes

Traditional microbiology analysis is usually hindered by the long time-cost and lack of portability in many urgent situations. In this work, we developed a novel electrochemical DNA biosensor (E-biosensor) for sensitive analysis of the 16S rRNA gene of five bacteria, using a consecutive adenine (polyA) probe. The polyA probe consists of a polyA tail and a recognition part. The polyA tail can combine onto the gold surface with improved controllability of the surface density, by conveniently changing the length of polyA. The recognition part of the capture probe together with two biotin-labeled reporter probes hybridize with the target DNA and form a stable DNA-tetramer sandwich structure, and then avidin-HRP enzyme was added to produce a redox current signal for the following electrochemical detection. Finally, we realized sensitive quantification of artificial target DNA with a limit of detection (LOD) of 10 fM, and excellent selectivity and reusability were also demonstrated. Importantly, the detection capability was equally good when facing bacterial genomic DNA, due to the base-stacking force of our multireporter-probe system, which can help to break the second structure and stabilize the probe-target complexes. Our biosensor was constructed on a 16-channel electrode chip without any polymerase chain reaction (PCR) process needed, which took a significant step toward a portable bacteria biosensor.

Point-of-Need DNA Testing for Detection of Foodborne Pathogenic Bacteria

Foodborne pathogenic bacteria present a crucial food safety issue. Conventional diagnostic methods are time-consuming and can be only performed on previously produced food. The advancing field of point-of-need diagnostic devices integrating molecular methods, biosensors, microfluidics, and nanomaterials offers new avenues for swift, low-cost detection of pathogens with high sensitivity and specificity. These analyses and screening of food items can be performed during all phases of production. This review presents major developments achieved in recent years in point-of-need diagnostics in land-based sector and sheds light on current challenges in achieving wider acceptance of portable devices in the food industry. Particular emphasis is placed on methods for testing nucleic acids, protocols for portable nucleic acid extraction and amplification, as well as on the means for low-cost detection and read-out signal amplification.

Superparamagnetic nanoarchitectures for disease-specific biomarker detection

Synthesis, bio-functionalization, and multifunctional activities of superparamagnetic-nanostructures have been extensively reviewed with a particular emphasis on their uses in a range of disease-specific biomarker detection and associated challenges.

Bacterial Analysis Using an Electrochemical DNA Biosensor with Poly-Adenine-Mediated DNA Self-Assembly

The spatial arrangement of DNA probes on the electrode surface is of critical significance for the performance of electrochemical biosensors. However, rational control of the probe surface remains challenging. In this work, we develop a capture probe carrying a poly-adenine anchoring block to construct a programmable self-assembled monolayer for a "sandwich-type" electrochemical biosensor. We show that with a co-assembling strategy using a polyA capture probe and 6-mercapto-1-hexanol, the density of the probes on the gold electrode can be simply adjusted by the length of polyA. The electron-transfer effect and thus the hybridization efficiency can as well be optimized by tuning the polyA length. As a result, we obtained an excellent biosensor performance with a limit of detection as low as 5 fM for a synthetic DNA target. We demonstrate the practicability of this system by analyzing a PCR product from Escherichia coli genomic DNA (0.2 pg/μL). On the basis of the ideal electrochemical interface, our polyA-based biosensor exhibited excellent reusability and stability, which is important for potential applications in the onsite analysis for a wide range of targets.

Designed synthesis and surface engineering strategies of magnetic iron oxide nanoparticles for biomedical applications

Iron oxide nanoparticles (NPs) hold great promise for future biomedical applications because of their magnetic properties as well as other intrinsic properties such as low toxicity, colloidal stability, and surface engineering capability. Numerous related studies on iron oxide NPs have been conducted. Recent progress in nanochemistry has enabled fine control over the size, crystallinity, uniformity, and surface properties of iron oxide NPs. This review examines various synthetic approaches and surface engineering strategies for preparing naked and functional iron oxide NPs with different physicochemical properties. Growing interest in designed and surface-engineered iron oxide NPs with multifunctionalities was explored in in vitro/in vivo biomedical applications, focusing on their combined roles in bioseparation, as a biosensor, targeted-drug delivery, MR contrast agents, and magnetic fluid hyperthermia. This review outlines the limitations of extant surface engineering strategies and several developing strategies that may overcome these limitations. This study also details the promising future directions of this active research field.

Ultra-sensitive biosensor for K-ras gene detection using enzyme capped gold nanoparticles conjugates for signal amplification

In this study, an ultra-sensitive hairpin DNA-based electrochemical DNA biosensor for K-ras gene detection is described. Gold nanoparticles (Au-NPs) and horseradish peroxidase (HRP)-streptavidin capped Au-NPs (HAS) conjugates are used for signal amplification. Initially, hairpin DNA dually labeled with thiol at its 5' end and with biotin at its 3' end is immobilized on the surface of Au-NPs modified electrode, and the hairpin DNA is in a "closed" state; hence, the HAS conjugates are shielded from being approached by the biotin due to steric hindrance. However, in the presence of target DNA, the target DNA hybridizes with the loop structure of hairpin DNA and causes conformational change, resulting in biotin forced away from the electrode surface, thereby becoming accessible for the HAS conjugates. Thus, the HAS conjugates are linked to the electrode surface via the specific interaction between biotin and streptavidin. Electrochemical detection was performed in phosphate-buffered saline (PBS) containing tetramethylbenzidine (TMB) and H2O2. Under optimal conditions, the peak current differences (ΔI) are linear with the target DNA in the range from 0.1 fM to 1 nM with a detection limit of 0.035 fM. Furthermore, this biosensor also demonstrates its excellent specificity for single-base mismatched DNA.

A novel DNA nanosensor based on CdSe/ZnS quantum dots and synthesized Fe3O4 magnetic nanoparticles

Although nanoparticle-enhanced biosensors have been extensively researched, few studies have systematically characterized the roles of nanoparticles in enhancing biosensor functionality. This paper describes a successful new method in which DNA binds directly to iron oxide nanoparticles for use in an optical biosensor. A wide variety of nanoparticles with different properties have found broad application in biosensors because their small physical size presents unique chemical, physical, and electronic properties that are different from those of bulk materials. Of all nanoparticles, magnetic nanoparticles are proving to be a versatile tool, an excellent case in point being in DNA bioassays, where magnetic nanoparticles are often used for optimization of the hybridization and separation of target DNA. A critical step in the successful construction of a DNA biosensor is the efficient attachment of biomolecules to the surface of magnetic nanoparticles. To date, most methods of synthesizing these nanoparticles have led to the formation of hydrophobic particles that require additional surface modifications. As a result, the surface to volume ratio decreases and nonspecific bindings may occur so that the sensitivity and efficiency of the device deteriorates. A new method of large-scale synthesis of iron oxide (Fe₃O₄) nanoparticles which results in the magnetite particles being in aqueous phase, was employed in this study. Small modifications were applied to design an optical DNA nanosensor based on sandwich hybridization. Characterization of the synthesized particles was carried out using a variety of techniques and CdSe/ZnS core-shell quantum dots were used as the reporter markers in a spectrofluorophotometer. We showed conclusively that DNA binds to the surface of ironoxide nanoparticles without further surface modifications and that these magnetic nanoparticles can be efficiently utilized as biomolecule carriers in biosensing devices.

Transglutaminase-mediated in situ hybridization (TransISH) system: a new methodology for simplified mRNA detection

Detection and localization of specific DNA or RNA sequences in cells and tissues are of great importance for biological research, diagnosis, and environmental monitoring. However, the most common procedure for in situ hybridization employs laborious immunostaining techniques. In the present study, we report proof-of-concept for a new RNA-enzyme conjugated probe for the detection of mRNA on tissue sections with a simple procedure. An RNA probe modified with a specific dipeptide substrate of transglutaminase was prepared. Alkaline phosphatase was then covalently and site-specifically combined to the dipeptide-labeled RNA using microbial transglutaminase. The new RNA probe labeled with alkaline phosphatase was validated by in situ hybridization (ISH) and proved to be a sensitive and sequence specific probe for mRNA detection in tissues. The new transglutaminase-mediated ISH (TransISH) strategy is free from antigen-antibody reaction, leads to one-step signal amplification after hybridization, and thus will be widely applicable for highly sensitive nucleic acid detection.

A novel biosensor based on serum antibody immobilization for rapid detection of viral antigens

In this paper, we represent a label-free biosensor based on immobilization of serum antibodies for rapid detection of viral antigens. Human serum containing specific antibodies against Japanese encephalitis virus (JEV) was immobilized on a silanized surface of an interdigitated sensor via protein A/glutaraldehyde for electrical detection of JEV antigens. The effective immobilization of serum antibodies on the sensor surface was verified by Fourier transform infrared spectrometry and fluorescence microscopy. The signal of the biosensor obtained by the differential voltage converted from the change into non-Faradic impedance resulting from the specific binding of JEV antigens on the surface of the sensor. The detection analyzed indicates that the detection range of this biosensor is 1-10 μg/ml JEV antigens, with a detection limit of 0.75 μg/ml and that stable signals are measured in about 20 min. This study presents a useful biosensor with a high selectivity for rapid and simple detection of JEV antigens, and it also proposes the biosensor as a future diagnostic tool for rapid and direct detection of viral antigens in clinical samples for preliminary pathogenic screenings in the case of possible outbreaks.