Function of Graphene Oxide as the “Nanoquencher” for Hg2+ Detection Using an Exonuclease I-Assisted Biosensor

Mercury (II) sensing using a simple turn-on fluorescent graphene oxide based aptasensor in serum and water samples

A simple, highly sensitive, and selective fluorometric aptasensing platform based on aptamer and graphene oxide (GO) is proposed for the determination of mercury (II) ion (Hg2+). In the designed assay, two aptamer probes, a carboxy-fluorescein (FAM) labeled aptamer (aptamer A) and its complementary (aptamer B) with partial complement containing several mismatches and GO as the quencher were used. In the absence of Hg2+, both A and B aptamers were adsorbed on the surface of GO by π-π-stacking, leading to fluorescence quenching of FAM due to fluorescence resonance energy transfer (FRET). Upon exposure to Hg2+, the A and B aptamer strands bind Hg2+ and form T-Hg2+-T complexes, leading to the formation of a stable double-stranded aptamer. The double-stranded aptamer is detached from the GO surface, resulting in the recovery of FAM fluorescence. The fluorescence intensity (FI) of the developed sensor was correlated with the Hg2+ concentration under optimized experimental conditions in two wide linear ranges, even in the presence of 10 divalent cations as interferences. The linear ranges were obtained from 200.0 to 900.0 fM and 5.0 to 33.0 pM, a limit of detection (LOD) of 106.0 fM, and a limit of quantification (LOQ) of 321.3 fM. The concentration of Hg2+ was determined in five real samples containing three water and two serum samples, using spiking and standard addition methods and the results were compared with the spiked amounts and atomic absorption (AAS) as standard method respectively, with acceptable recoveries. Furthermore, in the standard addition method, to overcome the effects of matrix influence of real samples in quantitative predictions, the excitation-emission matrix (EEM) data for samples was simultaneously analyzed by multivariate curve resolution with alternating least squares (MCR-ALS) as a second-order standard addition method (SOSAM).

Dual-mode fluorescence and electrochemiluminescence sensors based on Ru-MOF nanosheets for sensitive detection of apoE genes

A fluorescence-electrochemiluminescence (FL-ECL) dual-mode sensor for apoE gene detection has been developed, leveraging the unique properties of ruthenium metal organic framework nanosheets (RuMOFNSs). The system utilizes the quenching effect of the Ru(bpy)32+ ECL signal by ferrocene, leading to the synthesis of a multi-electron electrical signal marker, bisferrocene. By immobilizing the P-DNA on RuMOFNSs, bisferrocene quenches both FL and ECL signals. The addition of T-DNA and the consequent formation of double-stranded DNA enable the ExoIII enzyme to excise the bisferrocene fragment, restoring the signals. The sensor demonstrates wide detection linear ranges (1 fM to 1 nM for FL and 0.01 fM to 10 pM for ECL) and remarkable sensitivity (0.048 fM for FL and 0.016 fM for ECL). The dual-mode design offers enhanced reliability through a self-correction feature, reducing false positives. Compared to single-mode sensors, the dual-mode sensor shows significant advantages. Real-world testing confirms the sensor's capacity for robust detection in actual samples, underscoring its promising application in early disease diagnosis. This innovative approach opens up avenues for multi-signal response sensors, offering significant potential for diagnostic technologies.

Development of a split G-quadruplex and DAPI-based fluorescent probe for Hg(II) and Pb(II) ions detection

A novel thymine- and guanine-rich oligonucleotide (ODN-7) was engineered explicitly for the detection of Hg(II) and Pb(II) by a single intercalated dye 4',6-diamidinyl-2-phenylindole (DAPI). Upon the introduction of Hg(II), a rapid formation of T-Hg(II)-T base pairs takes place, triggering the assembly of a split G-quadruplex structure, resulting in a strong fluorescence signal due to DAPI intercalating into the T-Hg(II)-T mismatch. The introduction of Pb(II) initiates an interaction with the split G-quadruplex, causing a significant conformational change in its structure. Consequently, the altered split G-quadruplex structure fails to facilitate the insertion of DAPI into the T-Hg(II)-T complexes, leading to fluorescence quenching. This strategy offers a straightforward means of detecting Hg(II) and Pb(II). Leveraging the split G-quadruplex, the ODN-7 sensor enables the detection limits (3σ) for Hg(II) and Pb(II) to reach an impressive low of 0.39 nM and 4.98 nM, respectively. It exhibited a favorable linear range of 0.39-900 nM for Hg(II) detection (R2 = 0.9993) and 4.98 nM-5 μM for Pb(II) determination (R2 = 0.9953), respectively. Furthermore, the proposed sensor had excellent selectivity for detecting Hg(II) and Pb(II). It was used in milk samples containing mixed Hg(II) and Pb(II) solutions, yielding recovery rates of 99.3-103.8% for Hg(II) detection and 100.1-104.1% for Pb(II) detection.

Recent Advances in the Application of Bionanosensors for the Analysis of Heavy Metals in Aquatic Environments

Heavy-metal ions (HMIs) as a pollutant, if not properly processed, used, and disposed of, will not only have an influence on the ecological environment but also pose significant health hazards to humans, making them a primary factor that endangers human health and harms the environment. Heavy metals come from a variety of sources, the most common of which are agriculture, industry, and sewerage. As a result, there is an urgent demand for portable, low-cost, and effective analytical tools. Bionanosensors have been rapidly developed in recent years due to their advantages of speed, mobility, and high sensitivity. To accomplish effective HMI pollution control, it is important not only to precisely pinpoint the source and content of pollution but also to perform real-time and speedy in situ detection of its composition. This study summarizes heavy-metal-ion (HMI) sensing research advances over the last five years (2019-2023), describing and analyzing major examples of electrochemical and optical bionanosensors for Hg2+, Cu2+, Pb2+, Cd2+, Cr6+, and Zn2+.

Carbon-Based Nanomaterials 3.0

Carbon-based nanomaterials are currently attracting a lot of interest in many fields, ranging from medicine and biotechnology to electronics, energy storage, and sensing applications [...]