Molecular beacons (MBs) are suitable molecules capable of turning on or modifying their light emission only after a molecular interaction with well-defined molecular targets [1]. MBs are formed by oligonucleotide sequences and are generally labelled at the two strand ends with a fluorophore F on one side and a quencher Q on the other side, and structured in a hairpin shape capable to emit fluorescence only in the presence of a complementary oligonucleotide sequence which opens the hairpin structure.
Extremely interesting is the use of this nanosensing probe at intracellular level, suitably coupled to intracellular cargos, for the detection of target nucleic acid - such as messenger RNA (mRNA) in cells - combining the ability of sensing specific nucleic acids with the pharmacological silencing activity preventing the overexpression of proteins associated to pathologic conditions and. Their capability to act as theranostic agents has been proved with a molecular beacon specific for survivin mRNA immobilised on polymethylmethacrylate nanoparticles able to promote survivin MB uptake in human A549 cells [2].
MBs can be also used in both fluorescence-based and SERS-based optical biosensors. In the first case, the molecular beacon capable to hybridize with the mRNA for the survivin was immobilised at the distal end of a fibre nanotip and the emitted fluorescence is modulated by the presence of the target.
In the second case the MB is used to provide a signal-off mechanism in a SERS-based biosensor for the detection of miRNA-183, a miRNA biomarker that is specific for chronic obstructive pulmonary disease. The oligonucleotide biorecognition element is immobilised on a SERS substrate on one end and labelled with a Raman reporter on the other end [3].
The purpose of this talk is to provide an exhaustive overview on the design, implementation and characterization of these complex nanostructures as optical sensing probes.