Biotin- and iminobiotin-bonded surfaces obtained by thiol–ene chemistry and subsequent modification with polyamines were characterized with respect to streptavidin-binding capacity and reversibility for photonic biosensing using X-ray photoelectron spectroscopy and Mach–Zehnder-interferometric sensors. The streptavidin–iminobiotin system was exploited for reversible multilayer deposition and determination of affinity constants on each layer.

We present amperometric sensors based on direct electron transfer enzyme (DET) for the detection of lactate, which is an important medical parameter present in blood and interstitial dermal fluid (ISF). For measurement in blood, we present aplanar screen-printedbiosensor withcarbon working electrodes, whilefor the intendedmeasurement in ISF, we investigated platinum-metallized epoxy microneedle sensors. On both sensor types a bioink was applied, consisting of a DET enzyme mixed with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). As second layer, a hydrogel layer is deposited to hold the enzyme on site. Local modification of the platinum microneedle sensors was performed by non-contact spotting. The developed modification enables the detection of lactate at a potential of 0 V with response times of 500-700 s. For carbon sensors, a limit of detection of 0.12 mM lactate was determined, and two linear ranges of 0.3-5 mM and 10-50 mM were observed with sensitivities of 319 and 9.6 nA/(mm2·mM), respectively. For locally modified platinum microneedle sensors two linear ranges of 0.3-2.5 mM and 5-30.5 mM were observed with sensitivities of 322.5 and 3.7 nA/(mm ² ·mM), respectively. Given the low sensitivities in the higher concentration range, saturation for carbon sensors and locally modified platinum microneedle sensors starts at 10 mM and 5 mM lactate, respectively. Thus, both sensors allow sensitive measurements in the lower concentration range. Current densities at saturating lactate concentration are higher on freshly prepared carbon electrodes with 1.80 μA/mm ² (10 mM) compared to platinum microneedle electrodes with 0.75 μA/mm ² (10 mM) with full electrode modification. For platinum microneedle electrodes with optimized, dried local microneedle modification a current density of 0.95 μA/mm2 (5 mM) was measured. Detection of lactate in whole blood was demonstrated on carbon sensors, showing increasing currents after exercise, correlating with higher blood lactate levels, measured with a test strip reference system.

A two-dimensional photonic crystal defect waveguide sensor based on CMOS-compatible silicon-on-insulator technology was designed for operation in aqueous solutions at a wavelength of 1.34 µm, by the use of the 3D Plane Wave Expansion and the Finite Difference Time Domain simulation method. An operation under water in this wavelength regime allows for a significantly smaller propagation loss in contrast to the state-of-the-art operation wavelength of photonic crystals at 1.55 µm. The sensor working principle is label-free and based on evanescent wave sensing exploiting the local refractive index change induced by the specific binding of target molecules to a capture molecules immobilized on the surface of the phontonic crystal structure. We experimentally proved the theoretical predications of our simulations and demonstrated the sensing functionality of the photonic crystal defect waveguide using the biotin-straptavidin binding system.