Abstract: A method for producing a silver colloid solution of highly stable resulting colloids includes adding an aqueous solution of a hydroxylamine salt to an aqueous solution of an alkali, and then dispersing into the mixture an aqueous solution of the metal ions, the hydroxylamine salt being selected such that the anion, when combined with the said metal ions, would form a metal salt having a very low solubility in water, wherein the metal ion solution is introduced into the mixture in such a manner that the metal ions are substantially dispersed throughout the mixture within one second. A maturing period, preferably at elevated temperatures, leads to a stable state.

Abstract: A method is described for producing a silver colloid solution comprised of highly stable resulting colloids, the method comprising: adding an aqueous solution of a hydroxylamine salt to an aqueous solution of an alkali, and then dispersing into the mixture an aqueous solution of the metal ions, the hydroxylamine salt being selected such that the anion, when combined with the said metal ions, would form a metal salt having a very low solubility in water, wherein the metal ion solution is introduced into the mixture in such a manner that the metal ions are substantially dispersed throughout the mixture within one second. A maturing period, preferably at elevated temperatures, leads to a stable state in which the characteristics of the colloid undergo no further changes, and it is preferred to make and store the colloid in a polystyrene container for greatest stability.

Abstract: A method is described for producing highly stable silver colloidal solutions by reducing silver nitrate with lithium citrate. In the method, the main steps consist of: (a) heating a first quantity of water to a first predetermined temperature; (b) adding a second quantity of silver nitrate to the water; (c) heating the mixture to a second predetermined temperature; (d) adding a third quantity of an aqueous lithium citrate solution to the mixture; (e) maintaining the mixture at the second predetermined temperature for a predetermined time; and (f) cooling the mixture. The mixing process is accompanied by constant stirring. The colloid exhibits high light-scattering properties and intense SERS or SERRS spectra with low background fluorescence levels and a long shelf life, making it particularly suitable for Raman spectroscopy.

Abstract: A method is described for producing a silver colloid solution comprised of highly stable resulting colloids, the method comprising: adding an aqueous solution of a hydroxylamine salt to an aqueous solution of an alkali, and then dispersing into the mixture an aqueous solution of the metal ions, the hydroxylamine salt being selected such that the anion, when combined with the said metal ions, would form a metal salt having a very low solubility in water, wherein the metal ion solution is introduced into the mixture in such a manner that the metal ions are substantially dispersed throughout the mixture within one second. A maturing period, preferably at elevated temperatures, leads to a stable state in which the characteristics of the colloid undergo no further changes, and it is preferred to make and store the colloid in a polystyrene container for greatest stability.

Abstract: The present invention relates to sensitive SE(R)RS based methods for detecting analytes such as explosives and drugs, which may be present in a sample at extremely low levels. The methods may be generally carried out in situ employing novel chemistry which is compatible with flow-cell technology and with time-scales and concentrations required for rapid and informative screening of large numbers of samples. The present invention also relates to novel compounds e.g. synthons and apparatus for use with the methods disclosed.

Abstract: A method is described for producing highly stable silver colloidal solutions by reducing silver nitrate with lithium citrate. In the method, the main steps consist of: (a) heating a first quantity of water to a first predetermined temperature; (b) adding a second quantity of silver nitrate to the water; (c) heating the mixture to a second predetermined temperature; (d) adding a third quantity of an aqueous lithium citrate solution to the mixture; (e) maintaining the mixture at the second predetermined temperature for a predetermined time; and (f) cooling the mixture. The mixing process is accompanied by constant stirring. The colloid exhibits high light-scattering properties and intense SERS or SERRS spectra with low background fluorescence levels and a long shelf life, making it particularly suitable for Raman spectroscopy.

Abstract: The present invention relates to sensitive SE(R)RS based methods for detecting analytes such as explosives and drugs, which may be present in a sample at extremely low levels. The methods may be generally carried out in situ employing novel chemistry which is compatible with flow-cell technology and with time-scales and concentrations required for rapid and informative screening of large numbers of samples. The present invention also relates to novel compounds e.g. synthons and apparatus for use with the methods disclosed.

Abstract: Immunoassay displacement methods for detecting (preferably identifying) the presence or amount of a target analyte (e.g. drug) in a sample comprising the steps of: (a) exposing the sample to a complex comprising an immobilized antibody capable of specifically binding the analyte, said antibody being specifically bound to a displacement agent, wherein said agent comprises: (I) an analyte analog capable of specifically binding the antibody, (ii) a surface enhanced resonance raman scattering (SERRS) or a surface enhanced raman scattering (SERS) active label, (iii) a SERRS or SERS surface-seeking group (e.g. benztriazole), whereby any analyte present in the sample causes the displacement of agent from the antibody; (b) exposing any displaced agent to a SERRS or SERS surface; and, (c) detecting any displaced agent associated with said surface using SERRS or SERS. In preferred forms of the invention several target analytes are detected from a single source or sample simultaneously.

Abstract: The invention relates to the detection of target nucleic acids or nucleic acid units in a sample, by obtaining a SER(R)S spectrum for a SER(R)S-active complex containing, or derived directly from, the target. The complex includes at least a SER(R)S-active label, and optionally a target binding species containing a nucleic acid or nucleic acid unit. In this detection method, the concentration of the target present in the SER(R)S-active complex, or of the nucleic acid or unit contained in the target binding species in the SER(R)S-active complex, is no higher than 10.sup.-10 moles per liter. Additionally or alternatively, one or more of the following features may be used with the method: i) the introduction of a polyamine; ii) modification of the target, and/or of the nucleic acid or nucleic acid unit contained in the target binding species, in a manner that promotes or facilitates its chemi-sorption onto a SER(R)S-active surface; iii) inclusion of a chemi-sorptive functional group in the SER(R)S-active label.

Abstract: A plastics material which contains a pigment composition comprising a pigment having adsorbed on its surface, or as a physical mixture, up to 10% by weight, based on the total weight of pigment composition of a coding compound which is a compound containing azo, azomethine or polycyclic chromophore and which has an absorption spectrum and a Raman spectrum different from that of the pigment.

Abstract: The present invention provides an ink which contains a SERS--active metal aggregate containing a Raman active compound.

Abstract: The invention provides a pigment composition comprising a pigment having adsorbed on its surface, or as a physical mixture, up to 10% by weight, based on the total weight of pigment composition of a coding compound which is a compound containing an azo, azomethine or polycyclic chromophore and which has an absorption spectrum and a Raman spectrum different from that of the pigment. The compositions are suitable for use in printing inks for security applications.