A reagentless DNA-based electrochemical silver(I) sensor for real time detection of Ag(I) - the effect of probe sequence and orientation on sensor response

Threonine Phosphorylation of an Electrochemical Peptide-Based Sensor to Achieve Improved Uranyl Ion Binding Affinity

We have successfully designed a uranyl ion (U(VI)-specific peptide and used it in the fabrication of an electrochemical sensor. The 12-amino acid peptide sequence, (n) DKDGDGYIpTAAE (c), originates from calmodulin, a Ca(II)-binding protein, and contains a phosphothreonine that enhances the sequence's affinity for U(VI) over Ca(II). The sensing mechanism of this U(VI) sensor is similar to other electrochemical peptide-based sensors, which relies on the change in the flexibility of the peptide probe upon interacting with the target. The sensor was systematically characterized using alternating current voltammetry (ACV) and cyclic voltammetry. Its limit of detection was 50 nM, which is lower than the United States Environmental Protection Agency maximum contaminant level for uranium. The signal saturation time was ~40 min. In addition, it showed minimal cross-reactivity when tested against nine different metal ions, including Ca(II), Mg(II), Pb(II), Hg(II), Cu(II), Fe(II), Zn(II), Cd(II), and Cr(VI). Its reusability and ability to function in diluted aquifer and drinking water samples were further confirmed and validated. The response of the sensor fabricated with the same peptide sequence but with a nonphosphorylated threonine was also analyzed, substantiating the positive effects of threonine phosphorylation on U(VI) binding. This study places emphasis on strategic utilization of non-standard amino acids in the design of metal ion-chelating peptides, which will further diversify the types of peptide recognition elements available for metal ion sensing applications.

Switching the aptamer attachment geometry can dramatically alter the signalling and performance of electrochemical aptamer-based sensors

Electrochemical aptamer-based (EAB) sensors, composed of an electrode-bound DNA aptamer with a redox reporter on the distal end, offer the promise of high-frequency, real-time molecular measurements in complex sample matrices and even in vivo. Here we assess the extent to which switching the aptamer terminus that is electrode-bound and the one that is redox-reporter-modified affects the performance of these sensors. Using sensors against doxorubicin, cocaine, and vancomycin as our test beds, we find that both signal gain (the relative signal change seen in the presence of a saturating target) and the frequency dependence of gain depend strongly on the attachment orientation, suggesting that this easily investigated variable is a worthwhile parameter to optimize in the design of new EAB sensors.

Oligonucleotide-Based Reusable Electrochemical Silver(I) Sensor and Its Optimization via Probe Packing Density

We report herein a selective, sensitive, and reusable electrochemical sensor for the detection of silver(I) ions. This sensor detects Ag⁺ through a structure-switching electrode-bound DNA by measuring the changes in the electron-transfer efficiency. A single-stranded DNA, featuring a methylene blue (MB)-tagged DNA hairpin structure, strategically provides selective binding for the silver-mediated coordination of cytosine-Ag⁺-cytosine complexes. The DNA-modified electrode produces a change in the electrochemical signal due to the redox current of the surface-confined MB tag. The "turn-on" signaling upon silver(I) ion binding could be attributed to a conformational change in the MB-tagged DNA from an open structure to a target-induced folding structure. Differential pulse voltammetry of the DNA-modified electrode showed that the MB reduction signal increased linearly with an increase in Ag⁺ concentrations in a range of 10-200 nM, with a detection limit of 10 nM. The structure-switching silver(I) ion sensor was amenable to regeneration by simply unfolding the electrode-bound MB-tagged DNA in 100 mM ethylenediaminetetraacetic acid, and it could be regenerated with no loss in signal gain upon subsequent silver(I) ion binding. We also demonstrated that by controlling the probe packing density on the electrode surface, the fabrication parameters can be varied to achieve optimal sensor performance.

Application of DNA-Nanosensor for Environmental Monitoring: Recent Advances and Perspectives

PURPOSE OF REVIEW

Environmental pollutants are threat to human beings. Pollutants can lead to human health and environment hazards. The purpose of this review is to summarize the work done on detection of environmental pollutants using DNA nanosensors and challenges in the areas that can be focused for safe environment.

RECENT FINDINGS

Most of the DNA-based nanosensors designed so far use DNA as recognition element. ssDNA, dsDNA, complementary mismatched DNA, aptamers, and G-quadruplex DNA are commonly used as probes in nanosensors. More and more DNA sequences are being designed that can specifically detect various pollutants even simultaneously in complex milk, wastewater, soil, blood, tap water, river, and pond water samples. The feasibility of direct detection, ease of designing, and analysis makes DNA nanosensors fit for future point-of-care applications.

SUMMARY

DNA nanosensors are easy to design and have good sensitivity. DNA component and nanomaterials can be designed in a controlled manner to detect various environmental pollutants. This review identifies the recent advances in DNA nanosensor designing and opportunities available to design nanosensors for unexplored pathogens, antibiotics, pesticides, GMO, heavy metals, and other toxic pollutant.

One-Step Synthesis of Tunable Zinc-Based Nanohybrids as an Ultrasensitive DNA Signal Amplification Platform

Herein, we demonstrated a one-step route for the manufacturing of polypyrrole (PPy)/zinc nanohybrids with tunable elemental composition and nanoscale component mixing resolution by using an ultrafast (within tens of seconds) microwave approach for ultrasensitive DNA biosensors. The zinc-based nanoparticles (i.e., MWPPy/ZnO and MWPPy/ZnS) were produced by loading zinc acetate (ZnAc₂) on PPy under the electromagnetic environment of a microwave with or without sulfur powder in one pot. Then, the signal amplification platforms were fabricated by modifying the glassy carbon electrode (GCE) with the obtained nanohybrids. It was found that both of the resultant MWPPy/ZnO and MWPPy/ZnS were suitable for ultrasensitive DNA molecule detection of the gastric carcinoma related PIK3CA gene ascribing to their unique hybrid nanostructures and surface characteristics. Experimental results revealed that the proposed GCE/MWPPy/ZnO sensor showed a linear range of 1.0 × 10^-10 to 1.0 × 10^-13 M. Notably, the GCE/MWPPy/ZnS sensor was endowed with promising DNA hybrid selection with a minimum concentration response of 1.0 × 10^-18 M. The corresponding detection limit was, respectively, found to be 2.90 × 10^-11 and 7.73 × 10^-21 M for MWPPy/ZnO- and MWPPy/ZnS-based biosensors. Furthermore, reliable determination of single-base and two-base mismatched DNA are more attractive, which greatly supported the application of the constructed zinc-based nanohybrids for the detection of single nucleotide polymorphism in genetic diseases, biological infectious pathogens, or warning against bio-warfare agents.

A phenanthro[9,10-d]imidazole-based AIE active fluorescence probe for sequential detection of Ag+/AgNPs and SCN- in water and saliva samples and its application in living cells

Ag⁺ and SCN^- play extremely important roles in the fields of the physiology and environment. In this work, on the basis of phenanthro[9,10-d]imidazole derivative (DIPIP) which can exhibit the aggregation-induced emission (AIE) properties in aqueous solution, we achieved a sequential on-off-on switch for Ag⁺ and SCN^- with high selectivity and sensitivity. A remarkable fluorescence quenching effect of Ag⁺ on the probe DIPIP was observed with 1:2 stoichiometry, Subsequently, the fluorescence intensity of in situ generated DIPIP-Ag⁺ ensemble was easily switched on after the interaction between Ag⁺ and SCN^-, which was attributed to the stronger affinity of SCN^- to capture Ag⁺. In particular, the extreme limits of detection (LOD) for Ag⁺ and SCN^- in standard solutions were as low as to be 74.5 nM and 7.8 nM, respectively. Furthermore, the probe DIPIP and the DIPIP-Ag⁺ ensemble could be used to detect Ag⁺ in the real water and SCN^- in smoker saliva samples, respectively. In addition, the sequential "on-off-on" fluorescence mode of DIPIP to Ag⁺ and SCN^- were also successfully applied in living HeLa cells.

Ultrasensitive detection of Ag(I) based on the conformational switching of a multifunctional aptamer probe induced by silver(I)

We for the first time confirmed that the low concentrations of Ag(I) could induce a silver specific aptamer probe (SAP) from a random coil sequence form to G-quadruplex structure. Thereby, a novel highly sensitive fluorescence strategy for silver(I) assay was established. The designed multifunctional SAP could act as a recognition element for Ag(I) and a signal reporter. The use of such a SAP can ultrasensitively and selectively detect Ag(I), giving a detection limit down to 0.64nM. This is much lower than those reported by related literatures. This strategy has been applied successfully for the detection of Ag(I) in real samples, further proving its reliability. Taken together, the designed SAP is not only a useful recognition and signal probe for silver, but also gives a platform to study the interaction of monovalent cations with DNA.

Simple preparation and highly selective detection of silver ions using an electrochemical sensor based on sulfur-doped graphene and a 3,3′,5,5′-tetramethylbenzidine composite modified electrode

An electrochemical sensor based on S-Gr-TMB/GCE was prepared to solve the nonselectivity problem of TMB as a spectral probe.

Editorial: Translating the advances of biosensors from bench to bedside

Biosensors have been found with numerous applications in many areas including genetic analysis, detection of infectious diseases, environmental monitoring and forensic analysis. We have witnessed rapid advances in this field, especially with the emergence of nanotechnology in the past decade.

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.