Reduced graphene oxide as a resonance light-scattering probe for thrombin detection using dual-aptamer-based dsDNA

Investigating Efficacy of Three DNA-Aptamers in Targeted Plasmid Delivery to Human Prostate Cancer Cell Lines

Selection of targeted and efficient carriers to deliver drugs and genes to cells and tissues is still a major challenge and to overcome this obstacle, aptamers conjugated to nanoparticles have been broadly examined. To assess whether polycation of aptamers can improve plasmid delivery efficacy, we investigated the effect of three DNA-aptamers (AS1411, WY-5a, and Sgs-8) conjugated to branched polyethylenimine (b-PEI; MW ∼25 kDa) with different combinations of gene (plasmid) for delivery to prostate cancer cell lines (DU145 and PC3). According to transfection assessments, the dual conjugation of aptamers (AS:WY) with b-PEI produced the best results and increased the efficiency of plasmid delivery to up to three folds compared to unmodified PEI. Surprisingly, triple aptamer arrangement not only reduced transfection ability but also showed cytotoxicity. While our results demonstrated potential synergistic effects of AS1411 and WY-5a aptamers for gene delivery, it is important to note that the present evidence relies on the aptamer and cell types.

A label-free electrochemical aptasensor based on platinum@palladium nanoparticles decorated with hemin-reduced graphene oxide as a signal amplifier for glypican-3 determination

An electrochemical aptasensor for highly sensitive detection of glypican-3 has been developed using the GPC3 aptamer as the biorecognition probe and H-rGO-Pt@Pd NPs as an electroactive reagent.

Label-free bioassay with graphene oxide-based fluorescent aptasensors: A review

Bioassays using a fluorophore and DNA aptamer have been extensively developed due to the ultrasensitivity of fluorophores and recognition ability of DNA aptamers. Conventional fluorescent aptamer-based sensors (aptasensors) require chemical labeling between the fluorophore and aptamer and is technologically impracical for various sensing and assay applications. A simple "mix and go" strategy has been introduced that uses label-free technology as a platform for sensor development. The biosensors comprise a fluorophore, a ssDNA aptamer, and eco-friendly graphene oxide (GO). In the absence of the sensor target, GO quenches the fluorescence of the fluorophore and single-strand DNA aptamer complex. When the target is added, the DNA aptamer conformationally turns into a duplex, G-quadruplexe, or other secondary structure. This structure change leads to release of GO by the fluorophore-aptamer-target complex, generating dramatic fluorescence recovery and amplification. With this sensing method, the DNA aptamer does not need to be chemically labeled. Therefore, flexible fluorophore indicators and ssDNA aptamers can be used in this label-free aptasensing strategy. In this review, we discuss various unlabeled fluorophores, including synthetic small molecular fluorophores and genetically encoded fluorescent proteins, as indicators for generating GO-based fluorescent DNA aptasensors for label-free bioassay.

Detection of Single Nucleotide Polymorphisms by Fluorescence Embedded Dye SYBR Green I Based on Graphene Oxide

The detection of single nucleotide polymorphisms (SNPs) is of great significance in the early diagnosis of diseases and the rational use of drugs. Thus, a novel biosensor based on the quenching effect of fluorescence-embedded SYBR Green I (SG) dye and graphene oxide (GO) was introduced in this study. The probe DNA forms a double helix structure with perfectly complementary DNA (pcDNA) and 15 single-base mismatch DNA (smDNA) respectively. SG is highly intercalated with perfectly complementary dsDNA (pc-dsDNA) and exhibits strong fluorescence emission. Single-base mismatch dsDNA (SNPs) has a loose double-stranded structure and exhibits poor SG intercalation and low fluorescence sensing. At this time, the sensor still showed poor SNP discrimination. GO has a strong effect on single-stranded DNA (ssDNA), which can reduce the fluorescence response of probe DNA and eliminate background interference. And competitively combined with ssDNA in SNPs, quenching the fluorescence of SG/SNP, while the fluorescence value of pc-dsDNA was retained, increasing the signal-to-noise ratio. At this time, the sensor has obtained excellent SNP resolution. Different SNPs detect different intensities of fluorescence in the near-infrared region to evaluate the sensor's identification of SNPs. The experimental parameters such as incubation time, incubation temperature and salt concentration were optimized. Under optimal conditions, 1 nM DNA with 0–10 nM linear range and differentiate 5% SNP were achieved. The detection method does not require labeling, is low cost, simple in operation, exhibits high SNP discrimination and can be distinguished by SNP at room temperature.

Self-assembled colloidal gold superparticles to enhance the sensitivity of lateral flow immunoassays with sandwich format

Background: Traditional lateral flow immunoassay (LFIA) based on 20-40 nm gold nanoparticles (AuNPs) as signal reporter always suffers from relatively low detection sensitivity due to its insufficient brightness, severely restricting its wide-ranging application in the detection of target analytes with trace concentration.

Methods: To address this problem, the self-assembled colloidal gold superparticles (GSPs) were synthesized as an improved absorption-dominated labeling probe for improving the sensitivity of sandwich LFIA. Five kinds of GSPs with the size ranging from 100 nm to 400 nm were synthesized by embedding hydrophobic AuNPs of size 12 nm as building blocks into the polymer nanobeads. The as-prepared GSPs were suggested as novel labeling probes of LFIA. The effects of the size of assembled GSPs on the sensitivity of sandwich LFIA was assessed, and the detection performance of GSPs-LFIA was further compared with traditional AuNPs-LFIA.

Results: The resultant GSPs showed extremely high light absorption but very low light scattering, which favor the absorption-dominated signal output in LFIA. Among them, the GSP₂₇₀-LFIA (size 270 nm) exhibits the highest sensitivity for human chorionic gonadotropin and hepatitis B surface antigen detection in real serum sample, which are approximate 39.79- and 13.8-fold higher than that of traditional AuNP₄₀-LFIA.

Conclusions: The proposed research demonstrated that the current GSPs can provide an ultrasensitive and quantitative detection for disease biomarkers in real serum samples as promising reporters of sandwich LFIA platform.

Hydrogel based aptasensor for thrombin sensing by Resonance Rayleigh Scattering

In this research, a novel Resonance Rayleigh Scattering (RRS) aptasensor was developed for thrombin monitoring using in-situ synthesized and embedded Au nanoparticles (AuNPs) into poly vinyl alcohol -borax hydrogel (PBH). Thiolated-thrombin binding aptamer (thiolated-TBA) was attached to the surface of AuNPs embedded into PBH to design the PBH-aptasensor for thrombin detection (thiolated-TBA@AuNPs-PBH). To verify the characteristic and morphology of PBH nanocomposite, energy dispersive X-ray analysis, TEM, average particle size analizer and UV-Vis spectra were performed. The difference in RRS intensities in the absence and presence of thrombin was calculated and selected as the monitoring signal. Effect of different parameters on the RRS signal was investigated at excitation wavelength of 500 nm. Under the approved conditions, the linear detection range was validated over the concentration of 0.70 pM- 0.02 μM. The limit of detection based on 3S_b was 0.10 pM. The relative standard deviation for 5.6 pM and 3.6 nM were 4.0 and 2.7% (n = 10), respectively. The proposed aptasensor was successfully applied as an experimental model for thrombin detection in serum samples of healthy volunteers with acceptable results.

Superwettable colloidal crystal micropatterns on butterfly wing surface for ultrasensitive detection

HYPOTHESIS

Ultrasensitive detections with enrichment approaches based on hydrophilic-hydrophobic patterns have attracted increasing attention in the early diagnosis and treatment of diseases. However, most of these techniques involve complicated micro-fabrications and chemical modifications to achieve their specific pattern substrate wettability. Hence, the development of a simple and effective approach for the construction of new surface wettability techniques for ultrasensitive detection is with great expectations.

EXPERIMENTS

We present a simple approach to fabricate the superwettable colloidal crystal (CC) micropatterns on superhydrophobic Morpho butterfly wing surface for the ultrasensitive detection. The superwettable CC micropatterns were easily obtained by infiltrating and self-assembling monodispersed silica colloidal nanoparticles on the plasma treated butterfly wing patterns. The analytes could be enriched onto the hydrophilic CC area due to the wettability difference between the hydrophilic CC area and the superhydrophobic substrate.

FINDINGS

It was demonstrated that the detection limit of thrombin was down to 1.8 × 10^-13 mol L^-1 based on the fluorophore-labeled aptamer. Moreover, with two-dimensional position codes of these CC micropatterns for different probes, the multiplex detection capability was also demonstrated with great accuracy. As the elimination of complex instruments and chemical modifications, this proposed platform offers a simple strategy for ultrasensitive multiplex detection in practical applications.

Proximity ligation assay induced and DNAzyme powered DNA motor for fluorescent detection of thrombin

A novel DNA motor for thrombin detection was described here based on proximity ligation assay (PLA) induced DNAzyme recycling cleavage. Fluorophore labeled DNA is modified on gold nanoparticles (AuNPs) and the fluorescent signal is quenched by AuNPs. The PLA between target thrombin and two aptamers induces the forming of Mg²⁺-dependent DNAzyme. The fluorophore labeled DNA is cleaved circularly by the DNAzyme, releasing the fluorescent fragment from AuNPs surface. The cleavage and rebinding process create a processive walking along AuNPs surface track. As a result, the fluorescent intensity recovers significantly. A good linear relationship is obtained between the ratio of fluorescence intensity and thrombin concentration in the range from 10 pM to 10 nM. The limit of detection is calculated to be 4 pM. These results are comparable or even better than other amplification based methods.

Design of an aptamer-based magnetic adsorbent and biosensor systems for selective and sensitive separation and detection of thrombin

An aptasensor was designed for sensitive detection of thrombin using in biological fluids by integrating a magnetic aptamer-microbeads. To achieve this goal, the surface of gold plated QCM crystals was coated with L-cysteine and a thrombin binding DNA aptamer was immobilized on the L-cysteine coated QCM crystals surface via glutaraldehyde coupling. The binding interactions of thrombin to QCM crystals were characterized. Magnetic poly(2-hydroxyethyl methacrylate-ethylene glycol dimethacrylate-vinylene carbonate), Mp(HEMA-EGDMA-VC) microbeads were synthesized and thrombin binding aptamer (TBA) was immobilized. The Mp(HEMA-EGDMA-VC)-TBA microbeads were effectively adsorbed thrombin from serum in a relatively short contact time (ca. 5.0 min), and the eluted protein from Mp(HEMA-EGDMA-VC)-TBA was transferred to the QCM aptasensor that showed a specific detection of thrombin from serum. The detection limit of thrombin using aptasensor was 1.00 nmol L^-1. The calculation dissociation constant of the aptasensor was 68.5 nmol L^-1. The selectivity of the aptasensor system was tested with three different proteins (i.e., elastin, immunoglobulin G (IgG) and human serum albumin (HSA)) and showed high specificity to thrombin. The aptasensor was regenerated by washing with NaOH solution, and repeatedly used until 20 cycles without a change in the performance.

Graphene oxide-based fluorometric determination of methicillin-resistant Staphylococcus aureus by using target-triggered chain reaction and deoxyribonuclease-assisted recycling

The authors describe a method for the fluorometric determination of methicillin-resistant Staphylococcus aureus (MRSA) by exploiting target-triggered chain reactions and deoxyribonuclease I (DNase I)-aided target recycling. It is making use of a carboxy-fluorescein (FAM)-labeled single-stranded probe containing two sections. One is complementary to the 5' terminus of the target, while the 3' terminus of the other target is adsorbed on the surface of graphene oxide (GO) via π-stacking interactions without the target (16S rRNA). This adsorption results in quenching of the fluorescence of the label and protects it from being cleaved by DNase I. However, upon addition of the target, DNA/RNA hybrids are repelled by GO. This leads to fluorescence recovery as measured at excitation/emission wavelengths of 480/514 nm due to a chain reaction that is triggered by the target. The signal is strongly amplified by using DNase I-mediated target recycling. The 16S rRNA of MRSA can be detected by this method in the 1 to 30 nM concentration range, and the detection limit is 0.02 nM. The method was applied to analyze bacterial samples, and the detection limit is as low as 30 CFU . mL^-1. The assay is highly sensitive and selective and in our percpetion has a large potential in diagnosis of drug-resistant bacteria. Graphical abstract Schematic of the graphene oxide-based fluorescent bioassay for Methicillin-resistant Staphylococcus aureus detection by using target-triggered chain reaction and deoxyribonuclease I-aided signal amplification.