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This protocol describes the synthesis and detailed calibration of a gold nanoparticle-based nanobeacon (Au-nanobeacon) as an innovative theranostic approach for detection and inhibition of sequence-specific DNA and RNA for in vitro and ex vivo applications. Under hairpin configuration, proximity to gold nanoparticles leads to fluorescence quenching; hybridization to a complementary target restores fluorescence emission due to the gold nanobeacons’ conformational reorganization that causes the fluorophore and the AuNP to part from each other. This concept can easily be extended and adapted to assist the in vitro evaluation of silencing potential of a given sequence to be later used for ex vivo gene silencing and RNAi approaches, with the ability to monitor real-time gene delivery action. The time range for the entire protocol is ~8 days, including synthesis, functionalization and calibration of Au-nanobeacons, RNAi and gene silencing assays.

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Antisense therapy is a powerful tool for post-transcriptional gene silencing suitable for down-regulating target genes associated to disease. Gold nanoparticles have been described as effective intracellular delivery vehicles for antisense oligonucleotides providing increased protection against nucleases and targeting capability via simple surface modification. We constructed an antisense gold-nanobeacon consisting of a stem-looped oligonucleotide double-labelled with 3′-Cy3 and 5′-Thiol-C6 and tested for the effective blocking of gene expression in colorectal cancer cells. Due to the beacon conformation, gene silencing was directly detected as fluorescence increases with hybridisation to target, which can be used to assess the level of silencing. Moreover, this system was extensively evaluated for the genotoxic, cytotoxic and proteomic effects of gold-nanobeacon exposure to cancer cells. The exposure was evaluated by two-dimensional protein electrophoresis followed by mass spectrometry to perform a proteomic profile and 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay, glutathione-S-transferase assay, micronucleus test and comet assay to assess the genotoxicity. This integrated toxicology evaluation showed that the proposed nanotheranostics strategy does not exhibit significant toxicity, which is extremely relevant when translating into in vivo systems.

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Aims: RNAi is a powerful tool for gene silencing that can be used to reduce undesirable overexpression of oncogenes as a novel form of cancer treatment. However, when using RNAi as a therapeutic tool there is potential for associated gene effects. This study aimed to utilize gold nanoparticles to deliver siRNA into HeLa cells. Results: Knockdown of the c-myc oncogene by RNAi, at the RNA, protein and cell proliferation level was achieved, while also identifying associated gene responses. Discussion: The gold nanoparticles used in this study present an excellent delivery platform for siRNA, but do note associated gene changes. Conclusion: The study highlights the need to more widely assess the cell physiological response to RNAi treatment, rather than focus on the immediate RNA levels.

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Identification of specific nucleic acid sequences mediated by gold nanoparticles derivatized thiol-modified oligonucleotides (Au-nanoprobes) has been proven to be a useful tool in molecular diagnostics. Here, we demonstrate that, on optimization, detection may be simplified via the use of a single Au-nanoprobe to detect a single nucleotide polymorphism (SNP) in homo- or heterozygote condition. We validated this non-cross-linking approach through the analysis of 20 clinical samples using a single specific Au-nanoprobe for an SNP in the FTO (fat mass and obesity-associated) gene against direct DNA sequencing. Sensitivity, specificity, and limit of detection (LOD) were determined, and statistical differences were calculated by one-way analysis of variance (ANOVA) and a post hoc Tukey's test to ascertain whether there were any differences between Au-nanoprobe genotyped groups. For the first time, we show that the use of a single Au-nanoprobe can detect SNP for each genetic status (wild type, heterozygous, or mutant) with high degrees of sensitivity (87.50%) and specificity (91.67%).

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Under laser radiation, cells labeled with gold nanoparticles (AuNPs) are believed to suffer thermal damage due to the transfer of the absorbed light from the AuNPs to the cells. This process, which involves complex mechanisms such as the rapid electron–phonon decay in the AuNPs, followed by phonon–phonon relaxation, culminates in the localized heating of both the AuNPs and the cells, setting the rational for the use of these nanostructures, under laser light, in cancer photothermal therapy (PTT). Here, we discuss the chemical and biological aspects of this promising new therapeutic approach, including the advantages over conventional cancer therapies and the challenges that scientists still need to overcome to progress toward translation research

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