A method for detecting the presence of an unbound portion of therapeutic agents in a bodily fluid sample, not bound to proteins if present in the bodily fluid sample, comprising: - providing a liquid sample comprising a bodily fluid and an unbound portion of a therapeutic agent, the bodily fluid comprising at least one endogenous component having a geometrical size larger than a geometrical size of the therapeutic agent, - providing a photonic integrated circuit comprising a porous material enrichment layer, a waveguide formed at least partially in the enrichment layer, and a blocking means provided on an outer surface of the enrichment layer, wherein the enrichment layer with blocking means is selectively permeable to facilitate penetration of the unbound portion of the therapeutic agent, wherein the waveguide is configured for inducing light-matter interaction between light guided in at least one optical mode of said waveguide and the unbound portion of the therapeutic agent in the enrichment layer, and further for collecting scattered light, resulting from said light-matter interaction, in said waveguide, and wherein the blocking means is configured to cooperate with the enrichment layer to maintain therapeutic agent access to the pores of the enrichment layer and prevent light-matter interaction between the at least one endogenous component and light guided in the waveguide, by hindering an adhesion of said endogenous component to a liquid-receiving surface of the enrichment layer with blocking means, which liquid-receiving surface is adapted for contacting the liquid sample, - contacting the liquid sample with the photonic integrated circuit, - illuminating an unbound portion of the therapeutic agent in the enrichment layer by supplying light to the waveguide, whereby light scattered by the therapeutic agent, in response to said illumination, is collected in the waveguide, - detecting a plurality of inelastic Raman scattering components in a power spectrum of the light collected by the waveguide, - comparing a spectral line strength of at least one of the plurality of inelastic Raman scattering components obtained for the therapeutic agent, to a predetermined threshold value to determine the presence of the unbound portion of the therapeutic agent. - providing a liquid sample comprising a bodily fluid and an unbound portion of a therapeutic agent, the bodily fluid comprising at least one endogenous component having a geometrical size larger than a geometrical size of the therapeutic agent, - providing a photonic integrated circuit comprising a porous material enrichment layer, a waveguide formed at least partially in the enrichment layer, and a blocking means provided on an outer surface of the enrichment layer, wherein the enrichment layer with blocking means is selectively permeable to facilitate penetration of the unbound portion of the therapeutic agent, wherein the waveguide is configured for inducing light-matter interaction between light guided in at least one optical mode of said waveguide and the unbound portion of the therapeutic agent in the enrichment layer, and further for collecting scattered light, resulting from said light-matter interaction, in said waveguide, and wherein the blocking means is configured to cooperate with the enrichment layer to maintain therapeutic agent access to the pores of the enrichment layer and prevent light-matter interaction between the at least one endogenous component and light guided in the waveguide, by hindering an adhesion of said endogenous component to a liquid-receiving surface of the enrichment layer with blocking means, which liquid-receiving surface is adapted for contacting the liquid sample, wherein the enrichment layer with blocking means is selectively permeable to facilitate penetration of the unbound portion of the therapeutic agent, wherein the waveguide is configured for inducing light-matter interaction between light guided in at least one optical mode of said waveguide and the unbound portion of the therapeutic agent in the enrichment layer, and further for collecting scattered light, resulting from said light-matter interaction, in said waveguide, and wherein the blocking means is configured to cooperate with the enrichment layer to maintain therapeutic agent access to the pores of the enrichment layer and prevent light-matter interaction between the at least one endogenous component and light guided in the waveguide, by hindering an adhesion of said endogenous component to a liquid-receiving surface of the enrichment layer with blocking means, which liquid-receiving surface is adapted for contacting the liquid sample, - contacting the liquid sample with the photonic integrated circuit, - illuminating an unbound portion of the therapeutic agent in the enrichment layer by supplying light to the waveguide, whereby light scattered by the therapeutic agent, in response to said illumination, is collected in the waveguide, - detecting a plurality of inelastic Raman scattering components in a power spectrum of the light collected by the waveguide, - comparing a spectral line strength of at least one of the plurality of inelastic Raman scattering components obtained for the therapeutic agent, to a predetermined threshold value to determine the presence of the unbound portion of the therapeutic agent.