Stabilization of Gold Nanoparticles by Hairpin DNA and Implications for Label-Free Colorimetric Biosensors

Theranostic DNA nanostructure based on phenotype-specific activation of antisense oligonucleotides

Antisense oligonucleotide (ASO) is a powerful agent for gene therapy, designed to form complementary pairs with specific mRNA to inhibit gene expression. However, low specificity limits its potential. To overcome this challenge, we developed a Y-shape DNA nanostructure that enhances the specificity in ASO-based treatment by introducing a detection trigger. The design incorporates the phenotype-specific miR21 activation and the sequential release of Bcl2 ASO. As a result, our Y-shape DNA nanostructure downregulates >50 % Bcl2 mRNA expression and induces >60 % cell death in breast cancer cells. Meanwhile, this approach shows no obvious damage to the non-cancerous cells, indicating the therapeutic potential as a theranostics agent in precision medicine with the combination of biomarker sensing and treatment. Overall, our Y-shape DNA nanostructure serves as a promising strategy providing potential in customized conformation design with specific target sequences in gene therapy.

Towards rational design: Developing universal freezing routes for anchoring DNA onto gold nanoparticles

DNA-functionalized gold nanoparticles (AuNPs), also known as spherical nucleic acids, are widely used in the development of biosensors, resulting in anchoring DNA onto AuNPs being a crucial preparation step and a popular research topic. The latest freeze-anchoring method is a simple and time-saving alternative to traditional salt aging; however, its universal applicability remains limited. In this study, we explored the interfacial interaction between DNA and the AuNP surface and proposed various universal routes for promoting freezing anchoring. Among them, rational design has been considered as the core idea to overcome these limitations, particularly using non-thiolated DNA anchoring, which offers significant advantages such as being unmodified, cost-effective, and easily accessible. We emphasize the importance of sequence structure and preparation process optimization, which mainly considers differences in DNA conformation and electrostatic repulsion. Additionally, the prepared DNA-functionalized AuNPs exhibited complete biological hybridization capability, and the extreme limiting conditions for non-thiolated DNA freeze anchoring were clarified. In summary, this study enhances our understanding of the interfacial relationship between DNA and AuNPs in the freeze-anchoring process and can significantly advance the applications of DNA-functionalized AuNP-based biosensors.

Label-free colorimetric detection of tetracycline using gold nanoparticles with different surface charge

Visual detection assay based on aptamer unmodified gold nanoparticles shows great potential in biotechnology. Here, we reported a visible, salt-free and highly sensitive tetracycline (TC) assay based on a colloidally stable mixture of AuNPs that contains poly (diallyl dimethylammonium chloride) capped AuNPs ((+)AuNPs) and tetracycline-specific aptamer capped AuNPs (Apt-capped AuNPs). This reported TC assay was visible and salt-free that did not need any salt during TC detection. With naked eyes, nanomolar tetracycline concentrations could be identified within 20 min. A detection limit of tetracycline down to a concentration of 1.0 fM with a broad detection range of 8 order of magnitudes (5 × 10-14 M to 5 × 10-6 M) was reached. Furthermore, the reported TC assay also exhibited good selectivity for tetracycline over other antibiotics, metal cations, proteins and amino acids. These findings clearly demonstrated the high potential of the reported TC assay for TC detection and monitoring.

Mercury-Mediated Epitaxial Accumulation of Au Atoms for Stained Hydrogel-Improved On-Site Mercury Monitoring

Trivalent Au ions are easily reduced to be zerovalent atoms by coexisting reductant reagents, resulting in the subsequent accumulation of Au atoms and formation of plasmonic nanostructures. In the absence of stabilizers or presence of weak stabilizers, aggregative growth of Au nanoparticles (NPs) always occurs, and unregular multidimensional Au materials are consequently constructed. Herein, the addition of nanomole-level mercury ions can efficiently prevent the epitaxial accumulation of Au atoms, and separated Au NPs with mediated morphologies and superior plasmonic characteristics are obtained. Experimental results and theoretical simulation demonstrate the Hg-concentration-reliant formation of plasmonic nanostructures with their mediated sizes and shapes in the presence of weak reductants. Moreover, the sensitive plasmonic responses of reaction systems exhibit selectivity comparable to that of Hg species. As a concept of proof, polymeric carbon dots (CDs) were used as the initial reductant, and the reactions between trivalent Au and CDs were studies. Significantly, Hg atoms prevent the epitaxial accumulation of Au atoms, and plasmonic NPs with decreased sizes were in situ synthesized, corresponding to varied surface plasmonic resonance absorption performance of the CD-induced hybrids. Moreover, with the integration of sensing substrates of CD-doped hydrogels, superior response stabilities, analysis selectivity, and sensitivity of Hg2+ ions were achieved on the basis of the mercury-mediated in situ chemical reactions between trivalent Au ions and reductant CDs. Consequently, a high-performance sensing strategy with the use of Au NP-staining hydrogels (nanostaining hydrogels) was exhibited. In addition to Hg sensing, the nanostaining hydrogels facilitated by doping of emerging materials and advanced chem/biostrategies can be developed as high-performance on-site monitoring routes to various pollutant species.

DNA Hairpins and Stabilization of Gold Nanoparticles: Effect of Stem Length and Toehold Composition

This study investigates the effect of DNA hairpins on the stabilization of gold nanoparticles (AuNPs) against salt-induced aggregation (SIA) in label-free colorimetric biosensors. AuNPs were incubated with DNA hairpins of varying stem lengths and toehold sequences, followed by the addition of NaCl, before being subjected to ultraviolet-visible (UV-vis) measurement. Results showed that hairpins with longer stems generally provide better stabilization of AuNPs (18-bp >14-bp >10-bp). No improvement was observed for 14- and 18-bp hairpins with a toehold beyond 8A, which may be attributed to saturated adsorption of hairpins on the gold surface. For 14-bp hairpins with an 8-mer homopolymeric toehold, we observed a stabilization trend of A > C > G > T, similar to the reported trend of ssDNA. For variants containing ≥50% adenine as terminal bases, introducing cytosine or guanine as preceding bases could also result in strong stabilization. As the proportion of adenine decreases, variants with guanine or thymine provide less protection against SIA, especially for guanine-rich hairpins (≥6G) that could form G-quadruplexes. Such findings could serve as guidelines for researchers to design suitable DNA hairpins for label-free AuNP-based biosensors.

Ultrasmall Pt Nanozymes Immobilized on Spherical Polyelectrolyte Brushes with Robust Peroxidase-like Activity for Highly Sensitive Detection of Cysteine

Distinct platinum (Pt) nanozymes as peroxidase mimics have received extensive interest owing to their outstanding catalytic activity, high environmental tolerance, lower consumption, and great potential in replacing natural enzymes. However, easy agglomeration of Pt nanoparticles (Pt NPs) resulting from the high surface free energy significantly decrease their peroxidase-like activity. Herein, spherical polyelectrolyte brush (SPB)-stabilized ultrasmall Pt NPs (SPB@Pt NPs) were prepared by a novel synthetic strategy where the SPB not only performed as a nanoreactor for the synthesis of ultrasmall Pt NPs but also greatly stabilized Pt NPs against aggregation. The well-defined SPB@Pt NP nanozymes exhibited outstanding peroxidase-like activity for the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB and were then used to establish a colorimetric sensor for rapid detection of cysteine, giving a limit of detection of 0.11 μM. Moreover, the colorimetric detection system was demonstrated with outstanding performance in sensitive and selective detection of cysteine in the presence of several interference molecules. From these results, SPB@Pt NPs have been regarded as promising peroxidase mimics for a large number of applications such as in biosensing, biomedicine, the food industry, and environmental chemistry.