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A quadruple-channel fluorescent sensor array based on label-free carbon dots (CDs) was fabricated to detect and discriminate a series of tetracyclines (TCs), including chlortetracycline (CTC), oxytetracycline (OTC), tetracycline (TC) and doxycycline (DOX).

We report a simple, facile, and reliable colorimetric system for detection of chromium(III) ions (Cr) using citrate- and thiourea-modified gold nanoparticles (AuNPs). The colorimetric sensing strategy is based on the synergistic coordination interaction of citrate and thiourea toward Cr on the surface of AuNPs, leading to the aggregation of AuNPs which produces a color change from red to purple. Under the optimal conditions, this colorimetric sensing system shows an excellent selectivity and sensitivity for Cr, and the limit of detection (LOD) is estimated to be 0.05 μM at a signal-to-noise ratio of 3, which is far below the current standard stipulated by U.S. Environmental Protection Agency (1.9 μM). Moreover, this LOD is one and a half orders of magnitude lower than those of previously reported modified AuNPs-based colorimetric methods. Visual color change can be observed when 50 μM of Cr was introduced to the sensing system. Furthermore, this colorimetric sensing system can be employed for detection of Cr in diluted natural water samples.

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