Surface-enhanced Raman scattering (SERS)-based cancer diagnostics is an important analytical tool in early detection of cancer. Current work in SERS focuses on plasmonic nanomaterials that suffer from coagulation, selectivity, and adverse biocompatibility when used in vitro, limiting this research to stand-alone biomolecule sensing. Here we introduce a label-free, biocompatible, ZnO-based, 3D semiconductor quantum probe as a pathway for in vitro diagnosis of cancer. By reducing size of the probes to quantum scale, we observed a unique phenomenon of exponential increase in the SERS enhancement up to ~106 at nanomolar concentration. The quantum probes are decorated on a nano-dendrite platform functionalized for cell adhesion, proliferation, and label-free application. The quantum probes demonstrate discrimination of cancerous and non-cancerous cells along with biomolecular sensing of DNA, RNA, proteins and lipids in vitro. The limit of detection is up to a single-cell-level detection.

A laser-induced periodic surface structure (LIPSS) has attracted research interest for its promising potential in micromachining for microelectronics and microelectromechanical systems. A femtosecond laser-induced periodical surface structure was investigated for polished crystalline silicon. The observed structure is similar to the classical ripples that are characterized by long, nearly parallel lines extending over the entire irradiated area on the metal and silicon surface after continuous or pulsed laser irradiation. The spacing of the ripples nearly equals the irradiation wavelength. The depth of these ripples increases nonlinearly with the fluence of irradiation. The orientation of these periodic structures is perpendicular to the vector of the electric field of the laser beam. It seemed that the pattern formed by a femtosecond laser complies well with conventional models. Unlike the patterns formed by a continuous or nanosecond pulsed laser, however, the spacing of the ripple formed by femtosecond pulses is not influenced by the incident angle of the laser beam. The formula used to predict the ripple spacing in the conventional model does not apply to the femtosecond laser induced ripple structure. A plausible explanation to this phenomenon is proposed. The effect of the pulse repetition rate was studied and it was found that a femtosecond laser oscillator generates the same periodic structure as the amplified laser system.

Cancer stem cells (CSC) can be identified by modifications in their genomic DNA. Here, we report a concept of precisely shrinking an organic semiconductor surface-enhanced Raman scattering (SERS) probe to quantum size, for investigating the epigenetic profile of CSC. The probe is used for tag-free genomic DNA detection, an approach towards the advancement of single-molecule DNA detection. The sensor detected structural, molecular and gene expression aberrations of genomic DNA in femtomolar concentration simultaneously in a single test. In addition to pointing out the divergences in genomic DNA of cancerous and noncancerous cells, the quantum scale organic semiconductor was able to trace the expression of two genes which are frequently used as CSC markers. The quantum scale organic semiconductor holds the potential to be a new tool for label-free, ultra-sensitive multiplexed genomic analysis.

In this article we report the synthesis of nanoparticles using femtosecond laser ablation with MHz pulse frequency at room temperature in air. Nanoparticles agglomerate by fusion, and form interweaving fibrous structures that show certain degree of self-assembly. It is found that there is a threshold-like pulse frequency at which fibrous nanoparticle aggregates start to form. The growth mechanism can be explained by existing theories regarding nanoparticle formation through femtosecond laser ablation. The threshold pulse frequency is in good agreement with the time to start nanoparticle formation, which has been derived numerically by previous analyses.