The effective detection of low-concentrated molecules in small volumes represents a significant challenge in many sectors such as biomedicine, safety, and pollution. Here, we show an easy way to dispense liquid droplets from few μl volume (0.2-0.5 μl) of a mother drop, used as reservoir, by using a pyro-electrohydro-dynamic jetting (p-jet) dispenser. This system is proposed for multi-purpose applications such as printing viscous fluids and as a biosensor system. The p-jet system is based on the pyroelectric effect of polar dielectric crystals such as lithium niobate (LN). The electric field generated by the pyroelectric effect acts electro-hydrodynamically on the sample of liquid, allowing the deposition of small volumes. The p-jet approach allows to obtain the dispensing of drops of very small volumes (up to tenths of a picoliter) avoiding the use of syringes and nozzles generally used in standard technologies. The reliability of the technique as a biosensor is demonstrated both in the case of oligonucleotides and in a sample of clinical interest, namely gliadin. The results show the possibility of detecting these biomolecules even when they are low abundant, i.e. down to attomolar. The results show a marked improvement in the detection limit (LOD) when compared with the conventional technique (ELISA). Moreover, it has been presented the possibility of using the p-jet as a useful tool in the detection of biomarkers, present in the blood but currently not detectable with conventional techniques and related to neurodegenerative diseases such as Alzheimer.
According to the International agency for Research on Cancer, cadmium (Cd) is considered as a human carcinogen. Cadmium may induce cell death by apoptosis in various cell types, although the underlying mechanisms are still unclear. Nowadays, the cytotoxic potential of heavy metals is commonly evaluated by different cellular endpoints as reactive oxygen species formation, cell viability or cell death. Heavy metals cytotoxicity testing is based on in-vitro methods such as MTT assay, for the colorimetric detection of mitochondrial activity, propidium iodide-staining of DNA, as cell death marker, fluorometric detection of ROS generation to evaluate the stress response and colorimetric detection of cytokine secretion for the inflammatory reaction by ELISA method. In this work, we present a label-free digital holography (DH) based technique as an in-vitro cytotoxicity assay, which overcomes the limitations of conventional in vitro test based on color or fluorescence read outs. In particular, we show how DH is able to quantify the evolution of key biophysical parameters of cells during the exposure to cadmium. Murine embryonic fibroblasts NIH 3T3 are chosen here as cellular model for studying the cadmium effects. The results demonstrate that DH is able to retrieve the temporal evolution of different key parameters such as cell volume, projected area, cell thickness and dry mass, thus providing a full quantitative characterization of the cell physical behaviour during cadmium exposure. This demonstrates DH as an elegant label-free tool for heavy metals toxicity analysis.