Dodecagonal plasmonic quasicrystals for phage-based biosensing.

In this work, we fabricate and characterize a novel sensitive two-dimensional surface enhanced Raman spectroscopy (SERS) substrate made of plasmonic nanocavities in a photonic quasicrystal arrangement characterized by a 12-fold rotational symmetry. Our SERS device is capable of detecting chemisorbed bacteriophages at a femtomolar range. Most importantly, the paper presents for the first time a study on the procedure to functionalize the plasmonic quasicrystal with bacteriophages of the Podoviridae family. The immobilization of the phages on the plasmonic substrate has been studied and verified through SERS measurements. A new stable peak, visible in the SERS spectra at 1326 cm-1 at a greater than 60 times amplification, confirms the immobilization of the phages on the substrate. This functionalization approach can be used also for other types of phages or plasmonic sensors and hence, our achievements could allow the development of novel systems for the specific detection of different species of bacteria.

Light-microgel interaction in resonant nanostructures.

Combination of responsive microgels and photonic resonant nanostructures represents an intriguing technological tool for realizing tunable and reconfigurable platforms, especially useful for biochemical sensing applications. Interaction of light with microgel particles during their swelling/shrinking dynamics is not trivial because of the inverse relationships between their size and refractive index. In this work, we propose a reliable analytical model describing the optical properties of closed-packed assembly of surface-attached microgels, as a function of the external stimulus applied. The relationships between the refractive index and thickness of the equivalent microgel slab are derived from experimental observations based on conventional morphological analysis. The model is first validated in the case of temperature responsive microgels integrated on a plasmonic lab-on-fiber optrode, and also implemented in the same case study for an optical responsivity optimization problem. Overall, our model can be extended to other photonic platforms and different kind of microgels, independently from the nature of the stimulus inducing their swelling.

Microgel assisted Lab-on-Fiber Optrode.

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.