Core-shell　silica　particles　encapsulating　two　luminescent　dyes　with　different　emission　wavelengths　were　prepared　for　ratiometric　fluorescence　sensing　of　pH.　The　composite　core-shell　structure　particles　contained　a　polyacrylonitrile　(PAN)　core　surrounding　a　silica　shell.　Fluorescein　isothiocyanate　(FITC)　encapsulated　in　the　silica　shell　was　taken　as　an　indicator,　Fluorescence　emission　from　Ru(dpp)3(ClO4)　2　immobilized　in　PAN　core　was　used　as　a　reference　light.　The　ratiometric　fluorescence　signal　from　the　core-shell　silica　particles　were　found　with　a　linear　range　from　pH　5.80　to　7.50　(R2　=　0.997).　In　addition,　the　morphology　of　the　core-shell　silica　particles,　the　effects　of　temperature　and　co-existing　substances　were　investigated.　The　core-shell　silica　particles　were　successfully　applied　to　determination　of　pH　value　in　water　and　urine　samples.　©　2012　The　Royal　Society　of　Chemistry.