Design of rapid, selective, and sensitive DNA and ribonucleic acid (RNA) biosensors capable of minimizing false positives from nuclease degradation is crucial for translational research and clinical diagnostics. We present proof-of-principle studies of an innovative micro-ribonucleic acid (miRNA) reporter-probe biosensor that displaces a self-complementary reporter, while target miRNA binds to the probe. The freed reporter folds into a hairpin structure to induce a decrease in the fluorescent signal. The self-complementarity of the reporter facilitates the reduction of false positives from nuclease degradation. Nanomolar limits of detection and quantitation were capable with this proof-of-principle design. Detection of miRNA occurs within 10 min and does not require any additional hybridization, labeling, or rinsing steps. The potential for medical applications of the reporter-probe biosensor is demonstrated by selective detection of a cancer regulating microRNA, Lethal-7 (Let-7a). Mechanisms for transporting the biosensor across the cell membrane will be the focus of future work.

Obtaining reproducible plasmon resonances from nanostars remains a challenge for both surfactant and surfactant-free syntheses. For any nanostar application, a plasmon band with a reproducible spectral profile and λ max is a fundamental criterion. In particular, synthesis of biocompatible gold nanostars will benefit from surfactant-free methods to alleviate concerns over the cytotoxicity of many surfactants used in current synthesis techniques and the relative ease of synthesis. In this paper, we analyze different surfactant-free nanostar synthesis conditions and their influence on achieving plasmon reproducibility. Plasmon reproducibility was judged via the standard deviation of the extinction spectra's λ max and the spectral bandwidth.The synthesis temperature was the most influential factor in producing gold nanostars with reproducible plasmons. Nanostars synthesized at 5 °C exhibited a statistically (α = 0.05) smaller standard deviation in both their λ max and spectral bandwidth than nanostars synthesized at 25 °C.The reproducibility of the plasmon band was preserved even when the reaction conditions were adjusted to shift the position of the peak plasmon resonance. The high reproducibility of this approach, combined with the ease of synthesis, presents a significant step towards achieving gold nanostars with reproducible plasmons for biological applications. For example, photodynamic therapy, biomedical imaging contrast agents, and biosensing will all benefit from the reproducibility of the nanostars plasmon bands.

Many microRNA biosensor platforms regard fluorescence signal generation as superior to quenching; however, the two methods are comparable rather than competitive.