Silicon nanoparticles were prepared by ultrafast laser ablation of a silicon target in deionized water. The nanoparticles were characterized by using optical absorption, Raman spectroscopy, and transmission electron microscopy. The mean size is found to vary from 60 to 2.5 nm in the absence of any reducing chemical reagents, decreasing the pulse energy value. High-resolution transmission electron microscopy together with Raman spectroscopy confirms the crystalline structure of the generated silicon nanoparticles. The energy confinement of carriers which is evaluated from optical experiments varies from 90 to 550 meV when the mean nanoparticles size decreases from 60 to 2.5 nm. In particular, the evaluated nanoparticle sizes from optical analysis and the LCAO theoretical model are found in agreement with transmission electron microscopy and Raman measurements for the silicon nanoparticles with a size less than 6 nm. Finally, we present stability studies which show that the smallest nanoparticles aggregate over time.

An investigation on the productivity of silicon nanoparticles by picosecond laser ablation in water is presented. A systematic experimental study is performed as function of the laser wavelength, fluence and ablation time. In case of ablation at 1064 nm silicon nanoparticles with a mean diameter of 40 nm are produced. Instead, ablation at 355 nm results in nanoparticles with a mean diameter of 9 nm for short ablation time while the mean diameter decreases to 3 nm at longer ablation time. An original model based on the in-situ ablation/photo-fragmentation physical process is developed, and it very well explains the experimental productivity findings. The reported phenomenological model has a general validity, and it can be applied to analyze pulsed laser ablation in liquid in order to optimize the process parameters for higher productivity. Finally, an outlook is given towards gram per hour yield of ultra-small silicon nanoparticles.

A picosecond laser ablation approach has been developed for the synthesis of ligand-free AuAg bimetallic NPs where the relative amount of Ag is controlled in situ through a laser shielding effect. Various measurements, such as optical spectroscopy, transmission electron microscopy combined with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry, revealed the generation of homogenous 15 nm average size bimetallic NPs with different compositions and tunable localized surface plasmon resonance. Furthermore, ligand-free metallic nanoparticles with respect to chemically synthesized nanoparticles display outstanding properties, i.e. featureless Raman background spectrum, which is a basic requirement in many plasmonic applications such as Surface Enhanced Raman Spectroscopy. Various molecules were chemisorbed on the nanoparticle and SERS investigations were carried out, by varying the laser wavelength. The SERS enhancement factor for AuAg bimetallic NPs shows an enhancement factor of about 5.7 × 10(5) with respect to the flat AuAg surface.

Several challenging biological sensing concepts have been realized using electrolyte-gated reduced graphene oxide field effect transistors (rGO-FETs). In this work, we demonstrate the interest of rGO-FET for the sensing of human papillomavirus (HPV), one of the most common sexually transmitted viruses and a necessary factor for cervical carcinogenesis. The highly sensitive and selective detection of the HPV-16 E7 protein relies on the attractive semiconducting characteristics of pyrene-modified rGO functionalized with RNA aptamer Sc5-c3. The aptamer-functionalized rGO-FET allows for monitoring the aptamer-HPV-16 E7 protein binding in real time with a detection limit of about 100 pg mL −1 (1.75 nM) for HPV-16 E7 from five blank noise signals (95% confidence level). The feasibility of this method for clinical application in point-of-care technology is evaluated using HPV-16 E7 protein suspended in saliva and demonstrates the successful fabrication of a promising field effect transistor biosensor for HPV diagnosis.

Biofunctionalized silicon quantum dots were prepared through a one step strategy avoiding the use of chemical precursors. UV-Vis spectroscopy, Raman spectroscopy and HAADF-STEM prove oligonucleotide conjugation to the surface of silicon nanoparticle with an average size of 4 nm. The nanoparticle size results from the size-quenching effect during in situ conjugation. Photoemissive properties, conjugation efficiency and stability of these pure colloids were studied and demonstrate the bio-application potential, e.g. for nucleic acid vector delivery with semiconducting, biocompatible nanoparticles.