Surface plasmon resonance imaging (SPRI) biosensors allow sensitive, real-time and label-free detection of biological species in fluids when they bound to the sensing surface. However, their sensitivity is now close to the theoretical limit. In particular, at ultra-low target concentration, the main limit is the diffusion of the biological target (protein, DNA, bacteria…) to the gold film surface. To locally increase the target concentration on the sensitive surface and overcome such diffusion limit, active mass transport of analytes can be induced by non-uniform electric fields using dielectrophoresis (DEP) and alternative-current electroosmosis (ACEO) flow. Depending on the frequency of the electric field applied and the conductivity of the suspension medium, DEP and ACEO can concentrate biological objects on electrodes. This work focuses on the trapping and the detection of bacteria. The gold film used for SPR imaging is also used as electrode for particle collection, after photolithography and wet etching. To obtain the most efficient electrode design, numerical simulations were performed to estimate the trapping force applied on bacteria in the fluidic chamber volume depending on the geometry of the electrodes. SPR biochips obtained were mounted in the Kretschmann configuration. Then, a DI water solution containing E.coli bacteria was injected in the fluidic chamber of the chip. AC voltage (10Vpp, 1 kHz) was applied. The arrival of bacteria on the sensing zone is monitored by a strong jump of the SPR signal when no signal was observed without mass transport. The easy integration of such DEP/ACEO-assisted SPR chips on commercial SPR benches makes them suitable fur ultralow detection of a wide range of biological species, from biomolecules to pathogens.
Surface Plasmon Resonance (SPR) biosensors are standard tools for chemical and biological sensing. They provide sensitive, real-time and label-free detection of biological species in fluids. However, their performance (time and detection threshold) is now close to the theoretical limit. In particular, at low target concentrations, sensitivity is limited by the diffusion of the target analyte to the sensor surface. To overcome the diffusion limit, non-uniform electric fields can be used to induce electrokinetic effects (dielectrophoresis and alternative-current electroosmosis) which attract analytes toward the surface sensing zone. This work proposes to pattern the gold film used for SPR detection and use it as electrodes for the electric field generation. The magnitude of the electrokinetic effects and resulting analyte trapping efficiency of different electrodes designs were studied numerically with COMSOL by modeling the dielectrophoretic and drag forces induced by the AC-electroosmotic flow. A biochip, which consists of a structured gold film on a glass substrate, was mounted in the SPR Kretschmann configuration in contact with a fluidic cell to enable the injection of analyte and rinsing solutions. SPR imaging allowed us to compare the spatial distribution of the SPR response both a planar metal zone similar to a conventional SPR sensor as well as on the electrodes. After microbeads injection into the fluidic cell and application an AC voltage (V=1Vpp, f=1kHz), a strong SPR signal jump was observed due to the analyte’s arrival on the sensing zone. As a result of the electrokinetic effects, the detection threshold of mass transport assisted SPR chips was improved by several orders of magnitude.
New ultrashort pulse laser systems exhibit an ever increasing performance which includes shorter pulses and higher
pulse energies. Optical components used in these systems are facing increasing requirements regarding their durability,
and therefore understanding of the damage mechanism is crucial. In the ultra-short pulse regime electron ionization
processes control the damage mechanisms. For the single wavelength, single pulse regime the Keldysh  and the Drude
model  allow a quantitative description of these ionization processes. However, in this model, the electrical field is
restricted to a single wavelength, and therefore it cannot be applied in the case of irradiation with two pulses at different
wavelengths. As frequency conversion is becoming more common in ultra-short pulse applications, further research is
needed in this field to predict the damage resistance of optical components. We investigate the damage behavior of high
reflective mirrors made of different metal oxide materials under simultaneous exposure to ultra-short pulses at the
wavelengths 387.5 nm and 775 nm, respectively.