Red and NIR active dipod–SDS self-assemblies for “turn on” quantification of spermine in serum, urine and food: smart-phone assisted on-site determination of spermine in amine-rich foods†

Spermine is a vital biomarker for clinical diagnosis of cancer and estimating food spoilage. Here, supramolecular assemblies of two donor–π–acceptor dipods R-SPM (λ_em 640 nm) and NIR-SPM (λ_em 720 nm) with SDS have been discovered for the detection of spermine and spermidine under physiological conditions at nanomolar levels. The addition of SDS to R-SPM and NIR-SPM results in the formation of self-assemblies (DLS, zeta-potential and UV-vis studies) with no significant change in their fluorescence but further addition of spermine/spermidine to the R-SPM∩SDS and NIR-SPM∩SDS assemblies results in a 30–80 fold increase in fluorescence intensity, respectively at 640 nm and 720 nm. The LOD for spermine and spermidine detection is 22 nM (4.4 ppb) and 67 nM (9.7 ppb). The ensembles show nominal interference from other biogenic amines, amino acids, metal ions, and anions. Both R-SPM∩SDS and NIR-SPM∩SDS ensembles can be stored in the dark for >3 months without affecting their performance. The potential of these ensembles for real world applications like analysis of spermine in urine, human serum and food spoilage in the case of cheese, mushrooms, chicken and mutton has been demonstrated. The smartphone relied RGB analysis facilitates the on-site determination of spermine in food samples.