Surface-enhanced Raman scattering: from the colloid to the stabile substrate

Supstrati za površinski pojaĉano Ramanovo raspršenje (SERS) pripremljeni su na tri razliĉita naĉina: (i) sintezom koloidnih suspenzija srebra, (ii) depozicijom srebra na prethodno elektrokemijski jetkan silicij i (iii) naparavanjem srebra na monosloj polistirenskih mikrosfera. Koloidne suspenzije sintetizirane su redukcijom srebrove soli (AgNO3) s razliĉitim reducirajućim sredstvima. Prvi tip ĉvrstih podloga dobiven je depozicijom metala na porozni silicij metodom uranjanja u otopinu AgNO3, nanošenjem koloidne suspenzije srebra ili postupkom pulsne laserske ablacije. Drugi tip ĉvrstih SERS supstrata dobiven je depozicijom monodisperznih polistirenskih sfera (350 i 1000 nm) u monosloju na hidrofilnu staklenu podlogu te naparavanjem razliĉitih debljina metalnih filmova pomoću evaporatora. Sve pripremljene podloge testirane su na SERS aktivnost korištenjem testnih molekula (piridin, rodamin 6G, metilensko modrilo). Za koloidnu suspenziju gdje je veliĉina Ag ĉestica iznosila oko 40 nm i uz korištenje natrijevog borhidrida kao agregirajućeg sredstva postignut je faktor pojaĉanja za piridin reda veliĉine 106. Za podloge bazirane na poroznom Si najniţe dobivene granice detekcije su 10-10 mol L-1 za metilensko modrilo (uz pobudu 633 nm) i 10-9 mol L-1 za rodamin 6G (uz pobudu 514,5 nm). Za supstrate bazirane na polistirenskim sferama najbolje postignute granice detekcije su 10-9 mol L-1 za rodamin 6G i 1,2 ×10-3 mol L-1 za piridin. Sintetizirane koloidne SERS podloge primijenjene su za određivanje niskih koncentracija histamina i aflatoksina B1.The substrates for surface enhanced Raman scattering (SERS) were prepared in three different ways: (i) the synthesis of silver colloidal suspension, (ii) the deposition of silver on the previously electrochemically etched silicon and (iii) vapor deposition of silver on a monolayer of polystyrene microspheres. Colloidal suspensions were synthesized by reduction of silver salts (AgNO3) with various reducing agents. The first type of solid substrates was obtained by the deposition of metal on the porous silicon using immersion plating method, by applying Ag colloidal solution or by pulsed laser ablation. Another type of solid SERS substrates was prepared by deposition of monodisperse polystyrene spheres (350 and 1000 nm) in a monolayer on a hydrophilic glass surface. Different thicknesses of metal films were evaporated on the substrates using e-beam deposition. All prepared substrates were tested for their SERS activity using the test molecules (pyridine, rhodamine 6G, methylene blue). For the colloidal suspension where the size of Ag particles was about 40 nm and with the use of sodium borohydride as aggregating agent the enhancement factor for pyridine of the order of 106 was reached. For the substrates based on porous Si the lowest limits of detection obtained were 10-10 mol L-1 for methylene blue (with 633 nm excitation) and 10-9 mol L-1 for rhodamine 6G (with 514.5 nm excitation). For substrates based on polystyrene spheres best achieved detection limits were 10-9 mol L-1 for rhodamine 6G and 1.2 × 10-3 mol L-1 for pyridine. Synthesized colloidal SERS substrates have been applied for the detection of low concentrations of histamine and aflatoxin B1