Novel dipole-enhancement mechanism and detection of high-sensitivity trace environmental hormone bisphenol A with LiCl as co-adsorbates using simple metal-nanoparticle-free solid SERS substrates

Some halogen ions (X = Cl-,Br-,I-) dissociated from alkali-metal-salt analyte (NaX(aq), KX(aq)) were used to enhance SERS signals in colloid substrates. The currently proposed mechanisms of halogen ions enhanced colloid SERS signals is the halogen ions as an aggregating agent to enhance analyte molecules on the hotspots. No effect of solid-state halogen salt on the solid SERS substrates is reported and remaining unclear. Here, a novel dipole-enhancement mechanism of new LiCl(s) salt addition to bisphenol A (BPA) of environmental hormone as co-adsorbates on solid SERS substrates is proposed, which exhibits the strong dipoles interaction of the solid state LiCl(s) with phenol and the better affinity of LiCl-BPA than BPA on the surface of substrate. The dipoles of solid-state LiCl(s) can attract the OH- bonds and benzene rings of BPA molecules, leading to specific amplification of those closer bonds. Also, LiCl interrupts the H-bonds of solution, resulting in better affinity and hydrophilicity, which enables nonspecific amplification of SERS spectra. A low concentration of 1 ppb BPA was detected by adding 1 wt% LiCl and a good coefficient of determination (R2 =0.9955) of BPA was achieved. Testing com-mercial plastic spoons and zipper bags with Bisphenol about 7.3 and 20.1 ppb were practically demonstrated.