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• Axial back-and-forth-reflection (BFR) inside capillary was investigated. • A photometer based on axial -BFR inside capillary was proposed. • Optical-path enhancement of axial -BFR is more efficient than that of radial -BFR. • In comparison with radial -BFR, axial -BFR features low transmission loss. • The photometer features high sensitivity, compact, low cost and easy fabrication. As for photometry analysis, increasing the optical-path (OP) via multi-reflection is an effective method for improving the detection sensitivity. In this paper, a photometer based on axial multi-reflection between two end-faces of capillary was proposed and investigated. The probe light can be back and forth reflected inside the capillary, by employing apertured silver-mirrors at both ends of a metal-capillary. With designed aperture profile (i.e., a central disc-aperture and a peripheral ring-aperture) of the mirror, a 4.2-fold enhancement on OP was realized (i.e., OP is 4.2 times the capillary length). Moreover, the photometer was applied to detecting nitrite with a detection limit of 1 nM, which exhibits 8.6~15 fold improvement compared with that of previous photometers with similar capillary length and the same chromogenic reagent without sample enrichment. The photometer features compact, low cost and easy fabrication. [ABSTRACT FROM AUTHOR]

• A compact and low-cost LIF based on pinhole metal-capillary (PMC) was proposed • The background signal (noise) can be effectively suppressed in PMC • The stringent requirement on laser beam-quality can be alleviated in PMC-LIF • An overall ~480 fold improvement on SNR was realized by using PMC and laser diode • A detection limit of 0.4 pM was realized for rhodamine B detection 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 ~480 fold improvement on SNR was realized, because the laser-sidewall 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 × 4 × 4 cm3), low-cost and high concentration detectability. [ABSTRACT FROM AUTHOR]