Carbon　dots　derived　from　citric　acid　and　amines　have　been　gaining　considerable　attention　due　to　their　high　quantum　efficiency,　but　there　are　researches　proven　the　presence　of　small　fluorescent　molecules　in　those　materials.　In　this　work,　with　proper　control　of　the　synthetic　conditions,　highly　fluorescent　5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyridine-7-carboxylic　acid　(TPCA)　as　nice　needle-like　crystals　were　harvested　by　a　simple　one-step　hydrothermal　method　directly　based　on　the　reaction　of　citric　acid　and　cysteamine　hydrochloride.　The　proposed　synthesis　route　does　not　need　extra　complicated　purification　process.　The　yield　of　TPCA　was　46.9%　and　the　quantum　yield　was　as　high　as　83.2%.　Experimental　results　confirmed　that　TPCA　possesses　all　advantages　of　carbon　dots　reported　previously　with　similar　starting　materials.　In　addition,　a　novel　and　effective　fluorescent　probe,　TPCA-Ag+,　was　designed　for　sensitive　and　selective　sensing　of　dopamine　(DA)　based　on　in-situ　formation　of　sliver　nanoparticles.　The　calibration　curve　for　DA　was　linear　up　to　0.4　mu　mol/L,　and　a　detection　limit　of　0.75　nmol/L　was　attained.　The　method　was　successfully　applied　to　the　determination　of　DA　in　dopamine　hydrochloride　injection　and　urine　samples　and　the　standard　addition　recoveries　were　in　a　range　of　87.2-102.8%.　(C)　2017　Elsevier　B.V.　All　rights　reserved.