Improvement of creatinine SERS detection using molecularly imprinted silica gel

Creatinine (CRN) is the component of human biofluids (urine, blood) which is a clinically important indicator for evaluation of various diseases, e.g., renal (dis)functions. This work is dedicated to application of molecularly imprinted silica gel (MISG) as a CRN-selective sorbent for solid phase extraction to improve SERS based detection of CRN in urine. MISG was prepared using sol-gel process in the presence of a template (CRN) and aluminum ions which served as a doping agent to create recognition sites. Spectrophotometry studies showed that the combination of doping and imprinting improves sorption capacity ~3 times. We found that doping plays a key role and imprinting without doping does not lead to sorption improvement at all. Hydroxylamine stabilized silver nanoparticles were used as SERS substrate and the maximal CRN signal (i.e., analysis sensitivity) was found in alkaline media. Also, addition of alkali leads to dissolution of MISG matrix that was used to release CRN molecules and speed-up of analysis by skipping elution step. SERS results also demonstrate that MISG possesses the maximal sorption in comparison with silica gels fabricated without imprinting and/or doping. Therefore, the final analysis protocol implies solid phase extraction of CRN from a solution with further pH adjusting of the MISG-CRN complex and SERS detection of the released CRN. The protocol testing using model CRN solution and a urine sample demonstrated possibility for CRN detection at physiologically relevant concentrations and significant reduction of SERS background after extraction step.