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MicroRNAs are associated with multiple cellular processes and diseases. Here, we designed a highly sensitive, magnetically retrievable biosensor using magnetic beads (MBs) as a model RNA sensor. The assay utilized two biotinylated probes, which were hybridized to the complementary target miRNA in a sandwich assay format. One of the biotinylated ends of the hybridization complex was immobilized onto the surface of a NeutrAvidin (NAV) coated MB and the other biotinylated end was conjugated to HRP via NAV-biotin interaction. The results were presented by colorimetric absorbance of the resorufin product from amplex red oxidation. We show that by combining the use of MBs as well as bio-specific immobilization, the sensitivity of miRNA detection is down to 100 pM. This model HRP-MBs system can be used for simple, rapid colorimetric quantification of low level DNA/RNA or other small molecules.

In this paper an inductive integrated sensor to be adopted in sensing application on microfluidic systems for biomedical applications is presented. It is based on the use of magnetic particles that, suitably coated, act as markers of the bio-molecule to be detected. The device consists of a primary coil and two secondary coils arranged in a differential configuration. The sensing principle of the device is related to the output voltage variation on the secondary coils due to the presence of the magnetic beads only over one of the two coils. A general transduction mechanism is therefore presented together with analytical models and some discussion on novel integrated devices whose layout is proposed here. These sensors will be embedded into a more general "lab on a chip" device in which suitable microfluidics will be implemented both to bind markers with analyte and to drive the fluid into the sensing chamber.