Application of electrochemical surface plasmon resonance spectroscopy for characterization of electrochemical DNA sensors

Combining plasmonic and electrochemical biosensing methods

The idea of combining electrochemical (EC) and plasmonic biosensor methods was introduced almost thirty years ago and the potential of electrochemical-plasmonic (EC-P) biosensors has been highlighted ever since. Despite that, the use of EC-P biosensors in analytics has been rather limited so far and the search for unique applications of the EC-P method continues. In this paper, we review the advances in the field of EC-P biosensors and discuss the features and benefits they can provide. In addition, we identify the main challenges for the development of EC-P biosensors and the limitations that prevent EC-P biosensors from more widespread use. Finally, we review applications of EC-P biosensors for the investigation and quantification of biomolecules, and for the study of biomolecular and cellular processes.

Facile construction of nanocubic Mn3[Fe(CN)6]2@Pt based electrochemical DNA sensors for ultrafast precise determination of SARS-CoV-2

Owing to the high mortality and strong infection ability of COVID-19, the early rapid diagnosis is essential to reduce the risk of severe symptoms and the loss of lung function. In clinic, the commonly used detection methods, including the computed tomography (CT) and reverse transcription-polymerase chain reaction (RT-PCR), are often time-consuming with bulky instruments, which normally require more than one hour to report the results. To shorten the analytical period for testing the COVID-19 virus (SARS-CoV-2), we proposed an ultrafast and ultrasensitive DNA sensors to achieve an accurate determination of the DNA sequence by the RNA reverse transcription (rtDNA) of the SARS-CoV-2. A nanocubic architecture of the MnFe@Pt crystals was constructed to integrate both electrocatalysis and conductivity to greatly improve the biosensing performance. After the immobilization of a specific capture and report DNA on above nanocomposite, the rtDNA can be rapidly caught to the DNA sensor to form a double-helix structure, thus generating the current signal change. Within only 10 min, the as-prepared DNA sensors exhibited ultralow detection limit (1 × 10-20 M) and wide linear detection range, together with an outstanding selectivity among various interfering substances.

Mesenchymal stem cell-based nanoparticles and scaffolds in regenerative medicine

Mesenchymal stem cells (MSCs) are adult stem cells owing to their regenerative potential and multilineage potency. MSCs have wide-scale applications either in their native cellular form or in conjugation with specific biomaterials as nanocomposites. Majorly, these natural or synthetic biomaterials are being used in the form of metallic and non-metallic nanoparticles (NPs) to encapsulate MSCs within hydrogels like alginate or chitosan or drug cargo loading into MSCs. In contrast, nanofibers of polymer scaffolds such as polycaprolactone (PCL), poly-lactic-co-glycolic acid (PLGA), poly-L-lactic acid (PLLA), silk fibroin, collagen, chitosan, alginate, hyaluronic acid (HA), and cellulose are used to support or grow MSCs directly on it. These MSCs based nanotherapies have application in multiple domains of biomedicine including wound healing, bone and cartilage engineering, cardiac disorders, and neurological disorders. This study focused on current approaches of MSCs-based therapies and has been divided into two major sections. The first section elaborates on MSC-based nano-therapies and their plausible applications including exosome engineering and NPs encapsulation. The following section focuses on the various MSC-based scaffold approaches in tissue engineering. Conclusively, this review mainly focused on MSC-based nanocomposite's current approaches and compared their advantages and limitations for building effective regenerative medicines.

Effects of redox label location on the performance of an electrochemical aptamer-based tumor necrosis factor-alpha sensor

We report the development of an electrochemical aptamer-based sensor for real time detection of tumor necrosis factor-alpha. The focus of this study is to evaluate the effects of the redox label location on the overall sensor performance, including sensor stability, detection limit, reusability, and selectivity. Three aptamer probes, each labeled with methylene blue (MB) at a specific location, were designed and employed in the fabrication of the sensors. Among the three sensors, the sensor fabricated using an aptamer with the MB label located at the distal end has a detection limit of 100 pM and is regenerable. The sensor fabricated using an aptamer with an internal MB modification has a detection limit of 10 nM and is not regenerable. Both sensors can be employed in complex biological samples such as 50% urine and 50% saliva. However, the sensor fabricated with an aptamer with the MB label located at the proximal end suffers from poor reproducibility and is highly unstable, thus limiting its application as a sensor. On the bases of these results, placing the MB label at the distal end of the aptamer probe appears to be the most advantageous for this sensor design for it does not interfere with monolayer formation and target binding.

Dual-Mode Electro-Optical Techniques for Biosensing Applications: A Review

The monitoring of biomolecular interactions is a key requirement for the study of complex biological processes and the diagnosis of disease. Technologies that are capable of providing label-free, real-time insight into these interactions are of great value for the scientific and clinical communities. Greater understanding of biomolecular interactions alongside increased detection accuracy can be achieved using technology that can provide parallel information about multiple parameters of a single biomolecular process. For example, electro-optical techniques combine optical and electrochemical information to provide more accurate and detailed measurements that provide unique insights into molecular structure and function. Here, we present a comparison of the main methods for electro-optical biosensing, namely, electrochemical surface plasmon resonance (EC-SPR), electrochemical optical waveguide lightmode spectroscopy (EC-OWLS), and the recently reported silicon-based electrophotonic approach. The comparison considers different application spaces, such as the detection of low concentrations of biomolecules, integration, the tailoring of light-matter interaction for the understanding of biomolecular processes, and 2D imaging of biointeractions on a surface.

Folding- and Dynamics-Based Electrochemical DNA Sensors

A number of electrochemical DNA sensors based on the target-induced change in the conformation and/or flexibility of surface-bound oligonucleotides have been developed in recent years. These sensors, which are often termed E-DNA sensors, are comprised of an oligonucleotide probe modified with a redox label (e.g., methylene blue) at one terminus and attached to a gold electrode via a thiol-gold bond at the other. Binding of the target to the DNA probe changes its structure and dynamics, which, in turn, influences the efficiency of electron transfer to the interrogating electrode. Since electrochemically active contaminants are less common, these sensors are resistant to false-positive signals arising from the nonspecific adsorption of contaminants and perform well even when employed directly in serum, whole blood, and other realistically complex sample matrices. Moreover, because all of the sensor components are chemisorbed to the electrode, the E-DNA sensors are essentially label-free and readily reusable. To date, these sensors have achieved state-of-the-art sensitivity, while offering the unprecedented selectivity, reusability, and the operational convenience of direct electrochemical detection. This chapter reviews the recent advances in the development of both "signal-off" and "signal-on" E-DNA sensors. Critical aspects that dictate the stability and performance of these sensors are also addressed so as to provide a realistic overview of this oligonucleotide detection platform.

Bioinspired Assemblies and Plasmonic Interfaces for Electrochemical Biosensing

Electrochemical biosensing represents a collection of techniques that may be utilized for capture and detection of biomolecules in both simple and complex media. While the instrumentation and technological aspects play important roles in detection capabilities, the interfacial design aspects are of equal importance, and often, those inspired by nature produce the best results. This review highlights recent material designs, recognition schemes, and method developments as they relate to targeted electrochemical analysis for biological systems. This includes the design of electrodes functionalized with peptides, proteins, nucleic acids, and lipid membranes, along with nanoparticle mediated signal amplification mechanisms. The topic of hyphenated surface plasmon resonance assays is also discussed, as this technique may be performed concurrently with complementary and/or confirmatory measurements. Together, smart materials and experimental designs will continue to pave the way for complete biomolecular analyses of complex and technically challenging systems.

Incorporation of extra amino acids in peptide recognition probe to improve specificity and selectivity of an electrochemical peptide-based sensor

We investigated the effect of incorporating extra amino acids (AA) at the n-terminus of the thiolated and methylene blue-modified peptide probe on both specificity and selectivity of an electrochemical peptide-based (E-PB) HIV sensor. The addition of a flexible (SG)3 hexapeptide is, in particular, useful in improving sensor selectivity, whereas the addition of a highly hydrophilic (EK)3 hexapeptide has shown to be effective in enhancing sensor specificity. Overall, both E-PB sensors fabricated using peptide probes with the added AA (SG-EAA and EK-EAA) showed better specificity and selectivity, especially when compared to the sensor fabricated using a peptide probe without the extra AA (EAA). For example, the selectivity factor recorded in the 50% saliva was ∼2.5 for the EAA sensor, whereas the selectivity factor was 7.8 for both the SG-EAA and EK-EAA sensors. Other sensor properties such as the limit of detection and dynamic range were minimally affected by the addition of the six AA sequence. The limit of detection was 0.5 nM for the EAA sensor and 1 nM for both SG-EAA and EK-EAA sensors. The saturation target concentration was ∼200 nM for all three sensors. Unlike previously reported E-PB HIV sensors, the peptide probe functions as both the recognition element and antifouling passivating agent; this modification eliminates the need to include an additional antifouling diluent, which simplifies the sensor design and fabrication protocol.

Comparison of Mannose, Ethylene Glycol, and Methoxy-Terminated Diluents on Specificity and Selectivity of Electrochemical Peptide-Based Sensors

We report the synthesis and application of three new antifouling diluents for the fabrication of an E-PB HIV sensor. Among the three thiolated antifouling diluents used in this study, the methoxy-terminated diluent (C6-MEG) is the most effective in alleviating both nonspecific binding and adsorption of matrix contaminants onto the sensor surface, especially when compared to the mannose- (C6-MAN) and ethylene-glycol-terminated (C6-EG) diluents. The sensor fabricated with C6-MEG has a specificity factor (∼13.5) substantially higher than the sensor passivated with only 6-mercapto-1-hexanol (∼1.5). It is functional even when employed directly in 25% serum, an achievement that has not been observed with this class of E-PB sensors. More importantly, incorporation of these antifouling diluents has negligible impact on other important sensor properties such as sensitivity and binding kinetics. This sensor passivation strategy is versatile and can potentially be used with other E-PB sensors, as well as surface-based sensors that utilize thiol-gold self-assembled monolayer chemistry.