Laser induced cavitation is one of the effective techniques to generate controlled cavitation bubbles, both for basic study and for applications in different fields of engineering and medicine. Unfortunately, control of bubble formation and symmetry is hardly achieved due to a series of concurrent causes. In particular, the need to focus the laser beam at the bubble formation spot leads, in general, to a conical region proximal to the light source where conditions are met for plasma breakdown. A finite sized region then exists where the electric field may fluctuate depending on several disturbing agents, leading to possible plasma fragmentation and plasma intensity variation. Such irregularities may induce asymmetry in the successive bubble dynamics, a mostly undesired effect if reproducible conditions are sought for. In the present paper, the structure of the breakdown plasma and the ensuing bubble dynamics are analyzed by means of high speed imaging and intensity measurements of the shockwave system launched at breakdown. It is found that the parameters of the system can be tuned to optimize repeatability and sphericity. In particular, symmetric rebound dynamics is achieved almost deterministically when a pointlike plasma is generated at the breakdown threshold energy. Spherical symmetry is also favored by a large focusing angle combined with a relatively large pulse energy, a process which, however, retains a significant level of stochasticity. Outside these special conditions, the elongated and often fragmented conical plasma shape is found to be correlated with anisotropic and multiple breakdown shockwave emission.

We report on the use of one-dimensional photonic crystals to detect clinically relevant concentrations of the cancer biomarker ERBB2 in cell lysates. Overexpression of the ERBB2 protein is associated with aggressive breast cancer subtypes. To detect soluble ERBB2, we developed an optical set-up which operates in both label-free and fluorescence modes. The detection approach makes use of a sandwich assay, in which the one-dimensional photonic crystals sustaining Bloch surface waves are modified with monoclonal antibodies, in order to guarantee high specificity during the biological recognition. We present the results of exemplary protein G based label-free assays in complex biological matrices, reaching an estimated limit of detection of 0.5 ng/mL. On-chip and chip-to-chip variability of the results is addressed too, providing repeatability rates. Moreover, results on fluorescence operation demonstrate the capability to perform high sensitive cancer biomarker assays reaching a resolution of 0.6 ng/mL, without protein G assistance. The resolution obtained in both modes meets international guidelines and recommendations (15 ng/mL) for ERBB2 quantification assays, providing an alternative tool to phenotype and diagnose molecular cancer subtypes.

In the present communication, we report on the exploitation of a Bloch surface wave-enhanced fluorescence scheme for the detection of Interleukin (IL)-10 in a protein-rich buffer mimicking a biological sample. IL-10 is a cytokine known for its potent anti-inflammatory and immunosuppressive effects. It is considered a valuable biomarker for prognostic prediction for both solid tumors and hematological malignancies, and recently, a distinguishing feature of hyperinflammation during severe viral infections. To demonstrate the validity of the technique, we transferred all the reagents and working concentrations used in a gold-standard technique, such as ELISA, to our assay, with a substantial reduction in the execution time and without using any enzymatic amplification during IL-10 recognition. We estimate a limit of detection (LoD) in terms of the concentration of IL-10 in solution of the order of 110 pg/mL (5.8 pM) with a 14% accuracy; in other terms, the presented technique is compatible with the assay range and resolution (1.6 pM) of commercial gold-standard ELISA kits. Moreover, such LoD successfully matches the concentrations reported in literature for IL-10 detection in COVID-19 patients, making the BSW-based sensors a viable solution for rapid and accurate screening of COVID-19-related molecules.

Optical biosensors based on one-dimensional photonic crystals sustaining Bloch surface waves are proposed to study antibody interactions and perform affinity studies. The presented approach utilizes two types of different antibodies anchored at the sensitive area of a photonic crystal-based biosensor. Such a strategy allows for creating two or more on-chip regions with different biochemical features as well as studying the binding kinetics of biomolecules in real time. In particular, the proposed detection system shows an estimated limit of detection for the target antibody (anti-human IgG) smaller than 0.19 nM (28 ng/mL), corresponding to a minimum surface mass coverage of 10.3 ng/cm². Moreover, from the binding curves we successfully derived the equilibrium association and dissociation constants (K_A = 7.5 × 10⁷ M⁻¹; K_D = 13.26 nM) of the human IgG–anti-human IgG interaction.

We report on the use of biochips based on one-dimensional photonic crystals sustaining Bloch surface waves to specifically detect target miRNA that is characteristic of hemorrhagic stroke (miR-16-5p) at low concentration in a buffer solution.