A “turn-on” electrochemical aptasensor for ultrasensitive detection of Cd2+ using duplexed aptamer switch on electrochemically reduced graphene oxide electrode

Novel oligonucleotide-based sorbent for the selective extraction of cadmium from serum samples

The objective was to develop a sorbent functionalized with aptamers for the selective extraction of cadmium from biological samples. Two oligonucleotide sequences reported in literature as specific to cadmium were covalently grafted on activated Sepharose, with grafting yields of 45%. Once the supports packed in cartridges, a thorough study of the percolation conditions favoring Cd(II) retention was performed, demonstrating the importance of the nature of this medium. A high selectivity was reached when applying the optimal conditions as a recovery of 85% was obtained using the sorbent functionalized with one of the specific aptamers and only 1% on the control sorbent grafted with a scramble sequence. A high specificity was also obtained as recoveries for most of other ions were lower than 15%. The capacity of this oligosorbent estimated to 180 ng of Cd(II) for 30 mg of support was perfectly adapted to the trace analysis of Cd(II). The extraction procedure was then applied to a serum sample which was first subjected to acid precipitation. The initial concentration of cadmium in the serum was estimated to 1.83 µg/L using standard addition method and an extraction yield of 75 ± 1.6% was measured. Comparison of these results with those obtained without oligoextraction (recovery of 57%) showed a significant reduction of matrix effects in ICP-MS thanks to the use of the oligosorbent, underlining its interest for a more reliable quantification of Cd(II). This result was confirmed by performing the oligoextraction protocol on a certified serum.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Recent Achievements in Electrochemical and Optical Nucleic Acids Based Detection of Metal Ions

Recently nucleic acids gained considerable attention as selective receptors of metal ions. This is because of the possibility of adjusting their sequences in new aptamers selection, as well as the convenience of elaborating new detection mechanisms. Such a flexibility allows for easy utilization of newly emerging nanomaterials for the development of detection devices. This, in turn, can significantly increase, e.g., analytical signal intensity, both optical and electrochemical, and the same can allow for obtaining exceptionally low detection limits and fast biosensor responses. All these properties, together with low power consumption, make nucleic acids biosensors perfect candidates as detection elements of fully automatic portable microfluidic devices. This review provides current progress in nucleic acids application in monitoring environmentally and clinically important metal ions in the electrochemical or optical manner. In addition, several examples of such biosensor applications in portable microfluidic devices are shown.

Terminal deoxynucleotidyl transferase associated with split G-quadruplex/hemin deoxyribozyme amplification detection for various contaminants in milk based on pregnancy test strip platform

Contaminant residue analysis in milk can provide essential assistance for safety quality and contamination level management of milk production, which is critical for safeguarding public health. In this study, the pregnancy test strip is employed to achieve multiple analytes detection based on the specific recognition of aptamer and terminal deoxynucleotidyl transferase associated with split G-quadruplex/hemin deoxyribozyme system. Through the subsequent enzyme catalyzed reaction, the detection signal can be further amplified to improve the sensitivity. The method does not need to assemble test strip, prepare and purify antibodies/haptens, nor design complex probe sequences. By coupling human chorionic gonadotrophin with DNA probes and combining magnetic separation technology, the targets can be determined via the test strip. Under the optimized conditions, the visual detection limits for mercury ion, bisphenol A, and penicillin are 1, 0.1 and 0.05 nM, respectively. The detection results show that the method displays good accuracy and practicability in spiked milk sample. The method presents a simple scheme, low cost as well as good design versatility, which demonstrates great application prospect for the sensitive, low-cost, and convenient detection of food matrices.

Application of Nanomaterial Modified Aptamer-Based Electrochemical Sensor in Detection of Heavy Metal Ions

Heavy metal pollution resulting from significant heavy metal waste discharge is increasingly serious. Traditional methods for the detection of heavy metal ions have high requirements on external conditions, so developing a sensitive, simple, and reproducible detection method is becoming an urgent need. The aptamer, as a new kind of artificial probe, has received more attention in recent years for its high sensitivity, easy acquisition, wide target range, and wide use in the detection of various harmful substances. The detection platform that an aptamer-based electrochemical biosensor (E-apt sensor) provides is a new approach for the detection of heavy metal ions. Nanomaterials are particularly important in the construction of E-apt sensors, as they can be used as aptamer carriers or sensitizers to stimulate or inhibit electrochemical signals, thus significantly improving the detection sensitivity. This review summarizes the application of different types of nanomaterials in E-apt sensors. The construction methods and research progress of the E-apt sensor based on different working principles are systematically introduced. Moreover, the advantages and challenges of the E-apt sensor in heavy metal ion detection are summarized.

A novel signal amplification biosensor for detection of Cd2+ based on asymmetric PCR

In this work, a novel signal amplification biosensor was utilized to detect Cd²⁺ based on asymmetric PCR. In the presence of Cd²⁺, it can bind with Cd²⁺-aptamer C1 which caused the complementary strand C2 to be released from double-stranded DNA C1-C2. Because the single-stranded C1 cannot be hydrolyzed by Exo III, it can be used as a template to take part in asymmetric PCR reaction. In the absence of Cd²⁺, the C1-C2 was digested by Exo III and no PCR template was left. During the experiment, an interesting phenomenon was found that the asymmetric PCR can obtain higher level of fluorescent signal than that of symmetric PCR. To the best of our knowledge, this is the first report of using asymmetric PCR to detect Cd²⁺. Through the asymmetric PCR amplification strategy, this biosensor had a low detection limit (19.93 nM) and a wide linear range (0-500 nM). Meanwhile, this biosensor showed a satisfactory selectivity and recovery rate.

Highly sensitive biosensor based on aptamer and hybridization chain reaction for detection of cadmium ions

In this work, a highly sensitive biosensor for detecting cadmium ions (Cd²⁺ ) was developed based on Cd²⁺ -specific DNA aptamer and hybridization chain reaction (HCR). The Cd²⁺ -aptamer (named S0) was used to recognize Cd²⁺ and trigger HCR reaction. Without Cd²⁺ , S0 initiated the HCR to form long nicked dsDNA structures to quench the fluorescence. Then, Cd²⁺ can bind with S0 to block HCR to recover fluorescence. This biosensor had high sensitivity with the detection limit of 0.36 nM and a linear range from 0 to 10 nM. Moreover, it showed a satisfactory selectivity and recovery rates.

Graphene Based Nanohybrid Aptasensors in Environmental Monitoring: Concepts, Design and Future Outlook

In view of ever-increasing environmental pollution, there is an immediate requirement to promote cheap, multiplexed, sensitive and fast biosensing systems to monitor these pollutants or contaminants. Aptamers have shown numerous advantages in being used as molecular recognition elements in various biosensing devices. Graphene and graphene-based materials/nanohybrids combined with several detection methods exhibit great potential owing to their exceptional optical, electronic and physicochemical properties which can be employed extensively to monitor environmental contaminants. For environmental monitoring applications, aptamers have been successfully combined with graphene-based nanohybrids to produce a wide range of innovative methodologies. Aptamers are immobilized at the surface of graphene based nanohybrids via covalent and non-covalent strategies. This review highlights the design, working principle, recent developmental advances and applications of graphene based nanohybrid aptasensors (GNH-Apts) (since January 2014 to September 2021) with a special emphasis on two major signal-transduction methods, i.e., optical and electrochemical for the monitoring of pesticides, heavy metals, bacteria, antibiotics, and organic compounds from different environmental samples (e.g., water, soil and related). Lastly, the challenges confronted by scientists and the possible future outlook have also been addressed. It is expected that high-performance graphene-based nanohybrid aptasensors would find broad applications in the field of environmental monitoring.

Versatile Sensing Platform of Innovative Copper Oxide Assisted Cu-Phenolic Coordination Nanosheet mediated Fluorophore tagged GT-rich SSA based Fluorescence ON-OFF Biosensor for Subsequent Detection of Cd2+ and S2− Ions

Increased levels of toxic metal/non-metal ions Cadmium (Cd2+) and Sulfide (S2−) in the environment can be detrimental to human health. Given the circumstances, the detection and measurement of Cd2+ and...

2D Materials-Based Aptamer Biosensors: Present Status and Way Forward

Current advances in constructing functional nanomaterials and elegantly designed nanostructures have opened up new possibilities for the fabrication of viable field biosensors. Two-dimensional materials (2DMs) have fascinated much attention due to their chemical, optical, physicochemical, and electronic properties. They are ultrathin nanomaterials with unique properties such as high surface-to-volume ratio, surface charge, shape, high anisotropy, and adjustable chemical functionality. 2DMs such as graphene-based 2D materials, Silicate clays, layered double hydroxides (LDHs), MXenes, transition metal dichalcogenides (TMDs), and transition metal oxides (TMOs) offer intensified physicochemical and biological functionality and have proven to be very promising candidates for biological applications and technologies. 2DMs have a multivalent structure that can easily bind to single-stranded DNA/RNA (aptamers) through covalent, non-covalent, hydrogen bond, and π-stacking interactions, whereas aptamers have a small size, excellent chemical stability, and low immunogenicity with high affinity and specificity. This review discussed the potential of various 2D material-based aptasensor for diagnostic applications, e.g., protein detection, environmental monitoring, pathogens detection, etc.

Development of Electrochemical Aptasensor for Lung Cancer Diagnostics in Human Blood

We describe the preparation and characterization of an aptamer-based electrochemical sensor to lung cancer tumor markers in human blood. The highly reproducible aptamer sensing layer with a high density (up to 70% coverage) on the gold electrode was made. Electrochemical methods and confocal laser scanning microscopy were used to study the stability of the aptamer layer structure and binding ability. A new blocking agent, a thiolated oligonucleotide with an unrelated sequence, was applied to fill the aptamer layer’s defects. Electrochemical aptasensor signal processing was enhanced using deep learning and computer simulation of the experimental data array. It was found that the combinations (coupled and tripled) of cyclic voltammogram features allowed for distinguishing between the samples from lung cancer patients and healthy candidates with a mean accuracy of 0.73. The capacitive component from the non-Faradic electrochemical impedance spectroscopy data indicated the tumor marker’s presence in a sample. These findings allowed for the creation of highly informative aptasensors for early lung cancer diagnostics.

From Small Molecules Toward Whole Cells Detection: Application of Electrochemical Aptasensors in Modern Medical Diagnostics

This paper focuses on the current state of art as well as on future trends in electrochemical aptasensors application in medical diagnostics. The origin of aptamers is presented along with the description of the process known as SELEX. This is followed by the description of the broad spectrum of aptamer-based sensors for the electrochemical detection of various diagnostically relevant analytes, including metal cations, abused drugs, neurotransmitters, cancer, cardiac and coagulation biomarkers, circulating tumor cells, and viruses. We described also possible future perspectives of aptasensors development. This concerns (i) the approaches to lowering the detection limit and improvement of the electrochemical aptasensors selectivity by application of the hybrid aptamer-antibody receptor layers and/or nanomaterials; and (ii) electrochemical aptasensors integration with more advanced microfluidic devices as user-friendly medical instruments for medical diagnostic of the future.

Highly sensitive fluorescence detection of tobacco mosaic virus RNA based on disodium 4,4′-diazidostilbene-2,2′-disulfonate tetrahydrate in situ reaction

A novel fluorescent turn-on method for TMV RNA via the reducing ability of an AA and DES in situ reaction was reported.