Terahertz waves probe weak chemical bonds and therefore can facilitate label-free and immobilization-free biochemical detection. However so far only a limited number of research groups were able to measure biochemical reaction in water at room temperature [1]. The standard Terahertz free-space measurement techniques have insufficient sensitivity to measure small relative dielectric permittivity changes at high water absorption level. The state-of-the-art Terahertz sensor technology developed at ETRO-IR (VUB) can resolve <0.1\% ethanol concentration in water, using only 10nL to 10mL sample volume. The sensor configuration [2] features a rectangular waveguide (any band between 10-500GHz), liquid container (e.g. a capillary tube) and a tuning element for optimizing sensitivity at the desired dielectric permittivity of a sample.The sensor has been successfully used to measure a number of biochemical processes. To demonstrate protein binding (see figure 1) two types of samples are measured at different concentrations: (a) lysozyme with binding nanobody and (b) lysozyme with non-binding nanobody. Binding nanobody binds specifically to lysozyme and non-binding – does not, but both nanobody proteins have very similar mass. The measured signal difference between two samples reaches maximum at 1:1 molar ratio between lysozyme and nanobody where in case of binding nanobodies all binding partners form a complex. Other measurement examples include in situ monitoring of lysozyme crystallization, real-time particle concentration measurement at the output of HPLC separation column, DNA concentration increase with each PCR amplification cycle.