For　laser-induced　fluorescence　(LIF),　the　SNR　and　related　concentration　detectability　was　severely　limited　by　background　signal　(noise).　Herein,　an　axial-excitation　LIF　based　on　pinhole　metal-capillary　(PMC)　and　direct　laser-diode　excitation　was　proposed.　An　overall　similar　to　480　fold　improvement　on　SNR　was　realized,　because　the　lasersidewall　interaction　(LSI)　and　related　background　signal　(noise)　can　be　effectively　suppressed　in　PMC　by　avoidance　of　laser　leakage　and　laser　contact　with　capillary　sidewall.　For　rhodamine　B　detection　without　sample　enrichment,　a　detection　limit　of　concentration　(DLC)　of　0.4　pM　was　obtained,　which　is　2.5　fold　lower　than　the　DLC　(1　pM)　of　commercial　LIFs　equipped　with　bulky　and　expensive　Ar+　laser.　For　selective　detection　of　Cu2+,　a　DLC　of　5　pM　was　realized,　which　is　more　than　40　fold　lower　than　that　of　previous　fluorimetry　detection　with　similar　quantum-dot　probe.　The　PMC-LIF　features　compact　(16　x　4　x　4　cm(3)),　low-cost　and　high　concentration　detectability.