Sphingosine-1-phosphate (S1P) is a bioactive sphingo-lipid with a broad range of activities coupled to its role in G-protein coupled receptor signalling. Monitoring of both intra and extra cellular levels of this lipid is challenging due to its low abundance and lack of robust affinity assays or sensors. We here report on fluorescent sensory core-shell molecularly imprinted polymer (MIP) particles responsive to near physiologically relevant levels of S1P and the S1P receptor modulator fingolimod phosphate (FP) in spiked human serum samples. Imprinting was achieved using the tetrabutylammonium (TBA) salt of FP or phosphatidic acid (DPPA•Na) as templates in combination with a polymerizable nitrobenzoxadiazole (NBD)-urea monomer with the dual role of capturing the phospho-anion and signalling its presence. The monomers were grafted from ca 300 nm RAFT-modified silica core particles using ethyleneglycol dimethacrylate (EGDMA) as crosslinker resulting in 10-20 nm thick shells displaying selective fluorescence response to the targeted lipids S1P and DPPA in aqueous buffered media. Potential use of the sensory particles for monitoring S1P in serum was demonstrated on spiked serum samples, proving a linear range of 18-60 µM and a detection limit of 5.6 µM, a value in the same range as the plasma concentration of the biomarker. Beyond their role to maintain the integrity of living cells, several lipids are indispensable factors in cellular signalling 1-4. Many diseases have been linked with individual lipid species or related metabolic disorders 5. In view of the dynamic nature of these processes the time and space resolved quantification of these molecules is crucial for both fundamental understanding and for developing improved diagnostic tests 6-9. Robust means of real-time lipid quantification in situ are still to be realized. This warrants the development of affinity probes e.g. immune-, receptor or aptamer-based sensors 10,11 , capable of continuously reporting the lipid levels in biofluids. Such probes would be particularly beneficial for monitoring sphingosine-1-phosphate (S1P) in blood or in living cells, a signalling lipid rapidly emerging as a biomarker for a variety of conditions comprising among others cancer 4 , multiple sclerosis 12 , cardiovascular disease 13 and Alzheimer´s disease 14. Of equal urgency are probes for fingolimod (FTY720), a sphingosine analog and S1P-receptor modulator used in the treatment of multiple sclerosis 15,16. Addressing the robustness issue of biological receptors, lipid recognition elements in the form of macrocyclic hosts have been reported 17-20. However, these typically lack the required target selectivity and are often synthetically challenging to make. Molecular imprinting offers a possible solution to these problems 21-30. Polymers (molecularly imprinted polymers = MIPs) are prepared in presence of a template, structurally resembling or identical to the target that the polymers are designed to bind. Following this step, the template is removed, leaving behind a binding sit...

Summary of advances in synthesis and application of optical ratiometric nano- and microparticle sensors for in vitro and in vivo detection of pH, oxygen, ROS, ions, and biomarkers in cell microenvironment.