We describe an innovative experimental and computational approach to control the expression of a protein in a population of yeast cells. We designed a simple control algorithm to automatically regulate the administration of inducer molecules to the cells by comparing the actual protein expression level in the cell population with the desired expression level. We then built an automated platform based on a microfluidic device, a time-lapse microscopy apparatus, and a set of motorized syringes, all controlled by a computer. We tested the platform to force yeast cells to express a desired fixed, or time-varying, amount of a reporter protein over thousands of minutes. The computer automatically switched the type of sugar administered to the cells, its concentration and its duration, according to the control algorithm. Our approach can be used to control expression of any protein, fused to a fluorescent reporter, provided that an external molecule known to (indirectly) affect its promoter activity is available. A crucial feature of biological systems is their ability to maintain homeostasis in spite of ever-changing conditions. In engineering, this ability can be embedded in devices ranging from the thermostat to the autopilot of a modern plane using control systems which operate via a negative feedback mechanism: the quantity to be controlled is measured then subtracted from the desired reference value, and the resulting error is used to compute the control action to be implemented on the physical system (e.g. switching on or off the heating, changing the position of the rudder). Here, we developed and applied a method to regulate the expression level of a protein, in a growing population of cells over several generations, in a completely automatic fashion. We designed and implemented an integrated platform comprising a microfluidic device, a time-lapse microscopy apparatus, and a set of motorized syringes, all controlled by a computer. We tested the platform to force yeast cells to express a desired time-varying amount of a gene in yeast. Our method can be applied to control a protein of interest in vivo allowing to probe the function of biological systems in unprecedented ways.

This review summarizes the leading advancements in porous silicon (PSi) optical-biosensors, achieved over the past five years. The cost-effective fabrication process, the high internal surface area, the tunable pore size, and the photonic properties made the PSi an appealing transducing substrate for biosensing purposes, with applications in different research fields. Different optical PSi biosensors are reviewed and classified into four classes, based on the different biorecognition elements immobilized on the surface of the transducing material. The PL signal modulation and the effective refractive index changes of the porous matrix are the main optical transduction mechanisms discussed herein. The approaches that are commonly employed to chemically stabilize and functionalize the PSi surface are described.

In this work, we report on the light focusing ability exploited by the microshell of a marine organism: the Coscinodiscus wailesii diatom. A 100 µm spot size of a red laser beam is narrowed up to less than 10 µm at a distance of 104 µm after the transmission through the regular geometry of the diatom structure, which thus acts as a microlens. Numerical simulations of the electromagnetic field propagation show a good qualitative agreement with the experimental results. The focusing effect is due to the superposition of the waves scattered by the holes present on the surface of the diatom valve. Very interesting applications in micro-optic devices are feasible due to the morphological and biological characteristic of these unicellular organisms.

Complex micro- and nanostructured materials for optical sensing purposes are designed and fabricated using top technologies. A completely different approach to engineering systems at the nanoscale consists in recognizing the nanostructures and morphologies that nature has optimized during life’s history on earth. We have found that the photoluminescence emission from silica skeleton of marine diatoms Thalassiosira rotula Meunier is strongly dependent on the surrounding environment. Both the optical intensity and the peaks positions are affected by gases and organic vapors. Depending on the electronegativity and polarizing ability, some substances quench the luminescence, while others effectively enhance it. These phenomena allow the discrimination between different substances. These naturally occurring organisms are thus good candidates as optical sensing materials.