An electrochemical biosensor for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles

Electrochemical Sensor Based on DNA Aptamers Immobilized on V2O5/rGO Nanocomposite for the Sensitive Detection of Hg(II)

We developed a sensor consisting of V2O5 nanorods and a reduced graphene oxide (rGO) nanocomposite (V2O5/rGO) with immobilized DNA aptamers (Apt-NH@V2O5/rGO) for the sensitive electrochemical detection of Hg (II). The V2O5 nanorods anchored on rGO nanosheets were synthesized using a hydrothermal method. The nanocomposite was analyzed by various powerful physical methods that include X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, the Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared spectroscopy (FTIR). The FE-SEM of V2O5 disclosed the nanorod-like structure and uniform anchoring of V2O5 on the rGO nanosheet. Moreover, the BET results showed that the V2O5/rGO nanocomposite possesses excellent porosity. Furthermore, a glassy carbon electrode (GCE) was modified with Apt-NH@V2O5/rGO and used for the electrochemical detection of Hg(II) by differential pulse voltammetry (DPV). The aptasensor exhibited excellent sensitivity and selectivity toward Hg(II) detection, with a limit of detection (LOD) of 5.57 nM, which is below the maximum permissible limit established by WHO for rivers (30 nM). The sensor also exhibited significant stability and good repeatability.

Ultrasensitive Electrochemical Biosensors Based on Allosteric Transcription Factors (aTFs) for Pb2+ Detection

Exposure to Pb2+ in the environment, especially in water, poses a significant threat to human health and urgently necessitates the development of highly sensitive Pb2+ detection methods. In this study, we have integrated the high sensitivity of electrochemical techniques with allosteric transcription factors (aTFs) to develop an innovative electrochemical biosensing platform. This biosensors leverage the specific binding and dissociation of DNA to the aTFs (PbrR) on electrode surfaces to detect Pb2+. Under the optimal conditions, the platform has a broad linear detection range from 1 pM to 10 nM and an exceptionally low detection threshold of 1 pM, coupled with excellent selectivity for Pb2+. Notably, the biosensor demonstrates regenerative capabilities, enabling up to five effective Pb2+ measurements. After one week of storage at 4 °C, effective lead ion detection was still possible, demonstrating the biosensor's excellent stability, this can effectively save the cost of detection. The biosensor also achieves a recovery rate of 93.3% to 106.6% in real water samples. The biosensor shows its potential as a robust tool for the ultrasensitive detection of Pb2+ in environmental monitoring. Moreover, this research provides new insights into the future applications of aTFs in electrochemical sensing.

A novel copper ion enhanced electrochemical DNA biosensor for the determination of epinephrine

A novel electrochemical biosensor was developed for the detection of epinephrine (EP) by immobilizing double-strand DNA (dsDNA) bound with copper ions on a gold electrode (Cu2+/dsDNA/MCH/AuE). The electrochemical behavior of EP at Cu2+/dsDNA/MCH/AuE was examined, and the results demonstrated a significant enhancement in the electrocatalytic oxidation peak current of EP due to the formation of a stable G-Cu(II)-G sandwich structure between Cu2+ and guanine at the modified electrode. The modification process of the electrode was characterized by scanning electron microscopy, infrared spectroscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. A study on the effect of pH in phosphate buffer solution on the electrochemical oxidation of EP indicated that the catalytic oxidation process was pH-dependent. A plot of catalytic current versus EP concentration exhibited a dual-linear relationship within two ranges: 1.0-12.5 μM and 12.5-1000.0 μM, with correlation coefficients of 0.995 and 0.997, respectively. The limit of detection was determined to be 47 nM (S/N = 3). According to the calculated Hill coefficient (0.99), it can be concluded that the electrocatalytic process followed the Michaelis-Menten kinetic mechanism. The maximum catalytic current Im was 25 μA, while the apparent Michaelis-Menten constant Km was 1.425 mM. These findings indicated excellent electrocatalytic activity of the modified electrode towards oxidation of EP. The developed biosensor successfully detected EP in spiked mouse serum as well as epinephrine hydrochloride injection with high selectivity, sensitivity, stability, and accuracy.

Highly sensitive detection of Pb2+ in the environment with DNAzyme and rolling circle amplification reaction

Lead (Pb2+) is a toxic heavy metal that can severely pollute the environment and cause harm to public health. Therefore, the prompt and accurate monitoring of lead levels in the environment is vital. In this study, a novel DNAzyme-based cascade signal amplification biosensor that could detect Pb2+ with high sensitivity was designed through the combination of the strand displacement reaction (SDR) and rolling circle amplification (RCA). When Pb2+ is absent, RCA is triggered under the synergistic action of T4 DNA ligase and phi29 DNA polymerase with an artificially fluorophore-labeled S-chains being released to replace the upstream products generated by repeated RCA, thereby restoring the quenched fluorescence and emitting a strong fluorescent signal. After adding Pb2+, 8-17 DNAzyme binds specifically to Pb2+ and catalyzes the cleavage of the rA site on a single-stranded DNA with artificially modified rA site to restrict the RCA. The designed sensor provides a linear detection range for Pb2+ from 25 pM to 1 µM, with a low limit of detection 8.3 pM. Significantly, this sensor still demonstrates satisfactory performance when used for detecting Pb2+ in environment samples (e.g., river water). We consider that our study can provide reference values and ideas for the development of heavy metal ion detection methods.

Nanomaterials and DNA multistranded structures: a treasure hunt for targeting specific biomedical applications

The advent in nanoscience and nanotechnology has enabled the successful synthesis and characterization of different nanomaterials with unique electrical, optical, magnetic and catalytic activities. However, with respect to sensing applications, nanomaterials intrinsically lack target recognition ability to selectively bind with the analyte. DNA, an important genetic material carrying biopolymer is polymorphic in nature and shows structural polymorphism, forming secondary/multistranded structures like hairpin, cruciform, pseudoknot, duplex, triplex, G-quadruplex and i-motif. Studies reported so far have suggested that these polymorphic structures have been targeted specifically for the treatment or diagnosis of various diseases. DNA is widely used in conjugation with nanomaterials for the development of nanoarchitectures due to its rigidity, sequence programmability and specific molecular recognition, which makes this biomolecule a treasure for designing of DNA based frameworks. These two entities (DNA and nanomaterials) can be used in association with each other, as their alliance can result into creation of novel assay platforms for different purposes, ranging from imaging, sensing and diagnostics to targeted delivery. In this review, we have discussed about the recent reports on association of various mutistranded/ polymorphic forms of DNA with nanomaterials. Furthermore, different applications using this versatile DNA-nanomaterial assembly has also been elaborated at length. This review aims to target the interests of scientists from various interdisciplinary fields, including biologists, chemists and nanotechnologists, who wish to gain an understanding of nano-fabrications using a plethora of DNA polymorphic forms.Communicated by Ramaswamy H. Sarma.

A ratiometric electrochemical sensor for detecting lead in fish based on the synergy of semi-complementary aptamer pairs and Ag nanowires@zeolitic imidazolate framework-8

This work describes the synergistic application of semi-complementary aptamer pairs and signals on-off ratio strategies on glassy carbon electrodes (GCE) for detecting lead ions (Pb²⁺) in fish. Gold nanoparticles (AuPNs) as the electrode substrate can provide added binding sites for the aptamers and improve the conductivity of the electrodes. Pb²⁺ aptamers containing ferrocene (Fc) molecules act as molecular recognizers in the sensing system. In the presence of target ions, Fc signals are affected by conformational changes of the aptamer. The "Ag nanowires@zeolitic imidazolate framework-8 with methylene blue (AgNWs@ZIF-8/MB)" can be semi-complementary to the Pb²⁺ aptamer after binding to single-stranded DNA (S₁). However, S₁/AgNWs@ZIF-8/MB self-assembled with Pb²⁺ aptamer (Apt) by hybridization incubation was quickly replaced by Pb²⁺ competitively, resulting in the loss of methylene blue (MB) signaling molecules. Hence, the internal reference signal (MB) and conformation change signal (Fc) comprise the ratio sensing system well. Morphology, spectroscopy, and electrochemistry methods have validated the modification and sensing behaviors. The used Apt has made considerable progress in analytical performance. In interference studies and stability checks, the ratio measurement signal I_Fc/I_MB is a more reliable signal than the single signal readout. Following a log-linear relationship, this sensor provides a wide linear range. Furthermore, the proposed sensor can be used to determine Pb²⁺ in fish samples, and the results agree with those obtained using ICP-MS and recovery tests.

Homogeneous voltammetric sensing strategy for lead ions based on aptamer gated methylthionine chloride@UiO-66-NH2 framework as smart target-stimulated responsive nanomaterial

Herein an innovative electrochemical method is proposed for the determination of lead ions (Pb²⁺) based on a homogeneous voltammetric (HVC) sensing strategy using an aptamer gated methylthionine chloride@UiO-66-NH₂ framework as a smart target-stimulated responsive material. The proposed HVC sensor exhibits excellent sensing performance: ultralow detection limit (0.166 pM) and wide linearity (5.0 pM-500.0 nM), simultaneously, it avoids electrodeposition processes and it is simple to modify the electrode compared to previous electrochemical methods for Pb²⁺ detection. Thus our method shows great potential in the highly efficient detection of Pb²⁺ and other heavy metal ions by simply altering the related specific aptamer.

Single Molecular Chelation Dynamics Reveals That DNA Has a Stronger Affinity toward Lead(II) than Cadmium(II)

Lead ions can bind to DNA via nonelectrostatic interactions and hence alter its structure, which may be related to their adverse effects. The dynamics of Pb²⁺-DNA interaction has not been well understood. In this study, we report the monomolecular dynamics of the Pb²⁺-DNA interaction using a magnetic tweezers (MT) setup. We found that lead cations could induce DNA compaction at ionic strengths above 1 μM, which was also confirmed by morphology characterization. The chelation behavior of the Pb²⁺-DNA and the Cd²⁺-DNA complex solutions after adding EDTA were compared. The results showed that EDTA chelated with the bound metal ions on DNA and consequently led to restoring the DNA to its original length but with different restoration speeds for the two solutions. The fast binding dynamics and the slower chelation dynamics of the Pb²⁺ scenario compared to that of Cd²⁺ suggested that Pb²⁺ was more capable to induce DNA conformational change and that the Pb²⁺-DNA complex was more stable than the Cd²⁺-DNA complex. The stronger affinities for DNA bases and the inner binding of lead cations were two possible causes of the dynamics differences. Three agents, including EDTA, sodium gluconate, and SDBS, were used to remove the bound lead ions on DNA. It was shown that EDTA was the most efficient, and sodium gluconate could not fully restore DNA from its compact state. We concluded that both EDTA and SDBS were good candidates to restore the Pb²⁺-bound DNA to its original state.

Nanomaterials as Promising Theranostic Tools in Nanomedicine and Their Applications in Clinical Disease Diagnosis and Treatment

In recent decades, with the rapid development of nanotechnology, nanomaterials have been widely used in the medical field, showing great potential due to their unique physical and chemical properties including minimal size and functionalized surface characteristics. Nanomaterials such as metal nanoparticles and polymeric nanoparticles have been extensively studied in the diagnosis and treatment of diseases that seriously threaten human life and health, and are regarded to significantly improve the disadvantages of traditional diagnosis and treatment platforms, such as poor effectiveness, low sensitivity, weak security and low economy. In this review, we report and discuss the development and application of nanomaterials in the diagnosis and treatment of diseases based mainly on published research in the last five years. We first briefly introduce the improvement of several nanomaterials in imaging diagnosis and genomic sequencing. We then focus on the application of nanomaterials in the treatment of diseases, and select three diseases that people are most concerned about and that do the most harm: tumor, COVID-19 and cardiovascular diseases. First, we introduce the characteristics of nanoparticles according to the excellent effect of nanoparticles as delivery carriers of anti-tumor drugs. We then review the application of various nanoparticles in tumor therapy according to the classification of nanoparticles, and emphasize the importance of functionalization of nanomaterials. Second, COVID-19 has been the hottest issue in the health field in the past two years, and nanomaterials have also appeared in the relevant treatment. We enumerate the application of nanomaterials in various stages of viral pathogenesis according to the molecular mechanism of the complete pathway of viral infection, pathogenesis and transmission, and predict the application prospect of nanomaterials in the treatment of COVID-19. Third, aiming at the most important causes of human death, we focus on atherosclerosis, aneurysms and myocardial infarction, three of the most common and most harmful cardiovascular diseases, and prove that nanomaterials could be involved in a variety of therapeutic approaches and significantly improve the therapeutic effect in cardiovascular diseases. Therefore, we believe nanotechnology will become more widely involved in the diagnosis and treatment of diseases in the future, potentially helping to overcome bottlenecks under existing medical methods.

Advances in the Functional Nucleic Acid Biosensors for Detection of Lead Ions

Lead ions (Pb²⁺) are destructive to the natural environment and public health, so the efficient detection of Pb²⁺ is particularly important. Although the instrumental analysis methods have high accuracy, they require high cost and precise operation, which limits their wide application. Therefore, many strategies have been extensively studied for detecting Pb²⁺ by biosensors. Functional nucleic acids have become an efficient tool in this field. This review focuses on the recent biosensors of detecting Pb²⁺ based on functional nucleic acids from 2010 to 2020, in which DNAzyme, DNA G-quadruplex and aptamer will be introduced. The biosensors are divided into three categories that colorimetric, fluorometric and electrochemical biosensors according to the different reported signals. The action mechanism and detection effect of each biosensor are explained. Finally, the present situation of nucleic acid biosensor for the detection of Pb²⁺ is summarized and the future research direction is prospected.

Review of recent progress on DNA-based biosensors for Pb2+ detection

Lead (Pb) is a highly toxic heavy metal of great environmental and health concerns, and interestingly Pb²⁺ has played important roles in nucleic acids chemistry. Since 2000, using DNA for selective detection of Pb²⁺ has become a rapidly growing topic in the analytical community. Pb²⁺ can serve as the most active cofactor for RNA-cleaving DNAzymes including the GR5, 17E and 8-17 DNAzymes. Recently, Pb²⁺ was found to promote a porphyrin metalation DNAzyme named T30695. In addition, Pb²⁺ can tightly bind to various G-quadruplex sequences inducing their unique folding and binding to other molecules such as dyes and hemin. The peroxidase-like activity of G-quadruplex/hemin complexes was also used for Pb²⁺ sensing. In this article, these Pb²⁺ recognition mechanisms are reviewed from fundamental chemistry to the design of fluorescent, colorimetric, and electrochemical biosensors. In addition, various signal amplification mechanisms such as rolling circle amplification, hairpin hybridization chain reaction and nuclease-assisted methods are coupled to these sensing methods to drive up sensitivity. We mainly cover recent examples published since 2015. In the end, some practical aspects of these sensors and future research opportunities are discussed.

A Non-Enzyme and Non-Label Sensitive Fluorescent Aptasensor Based on Simulation-Assisted and Target-Triggered Hairpin Probe Self-Assembly for Ochratoxin a Detection

The monitoring and control of mycotoxins has caused widespread concern due to their adverse effects on human health. In this research, a simple, sensitive and non-label fluorescent aptasensor has been reported for mycotoxin ochratoxin A (OTA) detection based on high selectivity of aptamers and amplification of non-enzyme hybridization chain reaction (HCR). After the introduction of OTA, the aptamer portion of hairpin probe H1 will combine with OTA to form OTA-aptamer complexes. Subsequently, the remainder of the opened H1 will act as an initiator for the HCR between the two hairpin probes, causing H1 and H2 to be sequentially opened and assembled into continuous DNA duplexes embedded with numerous G-quadruplexes, leading to a significant enhancement in fluorescence signal after binding with N-methyl-mesoporphyrin IX (NMM). The proposed sensing strategy can detect OTA with concentration as low as 4.9 pM. Besides, satisfactory results have also been obtained in the tests of actual samples. More importantly, the thermodynamic properties of nucleic acid chains in the monitoring platform were analyzed and the reaction processes and conditions were simulated before carrying out biological experiments, which theoretically proved the feasibility and simplified subsequent experimental operations. Therefore, the proposed method possess a certain application value in terms of monitoring mycotoxins in food samples and improving the quality control of food security.

Electrochemical detection of β-lactoglobulin based on a highly selective DNA aptamer and flower-like Au@BiVO4 microspheres

Beta-lactoglobulin is a natural milk protein and the main cause of infant milk allergy. In this work, a sensitive, selective and inexpensive electrochemical biosensor for the detection of β-lactoglobulin was developed. In this sensor, a DNA aptamer was used instead of an expensive antibody as the recognition group highly selective for β-lactoglobulin. The flower-like BiVO₄ microspheres were firstly found to have peroxidase mimic catalytic activity and used to amplify the electrochemical signal. The aptamer can bind β-lactoglobulin and fall off from the working electrode, after which the DNA2/Au/BiVO₄ probe can be fixed to the DNA1/AuNPs/ITO working electrode by the hybridization of DNA2 with DNA1. Therefore, a higher concentration of β-lactoglobulin leads to increased fabrication of the DNA2/Au/BiVO₄ probe on the surface of the working electrode, and thereby increases the electrochemical signal. This electrochemical biosensor exhibited a wide detection range from 0.01 to 1000 ng mL^-1, with a limit of detection (LOD) of 0.007 ng mL^-1, which indicates a good potential application in the field of food analysis.