Ratiometric fluorescent test paper based on silicon nanocrystals and carbon dots for sensitive determination of mercuric ions

Abstract

Classical dye absorption-based pH test papers are widely used to measure the degree of acidity of media for quantification or semi-quantification by the observation of the naked eye on the variation of colour. However, it remains a challenging task to extend portable and cheap methods to a wide range of analytes for accurate quantification. Here, we report a dosage-sensitive test paper for the assay of mercury ions (Hg2+) with wide colour evolution. The ratiometric fluorescent probe was prepared by mixing blue-emission silicon nanocrystals (Si NCs) and red-emission carbon dots (r-CDs). The Si NCs serve as the reaction site and the r-CDs as the internal reference. Upon the addition of Hg2+, the blue fluorescence of the Si NCs was quenched, while the red fluorescence of the r-CDs remained constant, resulting in the consecutive fluorescence colour changes from blue to orange red. The probe demonstrates high selectivity and sensitivity of the visualization assay of Hg2+ with a detection limit of 7.63 nM. Moreover, we printed the ratiometric fluorescence probe result onto a piece of filter paper to prepare a test paper, which represents an on-site, sensitive, rapid and cost-effective method for the visual determination of Hg2+ by the naked eye.

Carbon Dots and a CdTe Quantum Dot Hybrid-Based Fluorometric Probe for Spermine Detection

“…Moreover, most of them adopted fluorescence intensity change as the signal output, which is usually affected by a number of factors such as the efficiency of instruments, the concentration of probe, and the external quenchers . In contrast, the ratiometric fluorescent probe possessing two individual fluorescence peaks could greatly reduce the above limitations by self-calibration, resulting in fluorescent color change of the probe and easy recognition under UV light irradiation. − Furthermore, the fluorescent paper prepared by dropping the fluorescent probe solution onto a paper-based substrate for the visualization assay demonstrated its effectiveness in terms of low cost, portable feasibility, and easy operation. − …”

Advances in Carbon Dot-Based Ratiometric Fluorescent Probes for Environmental Contaminant Detection: A Review

“…The detection and quantification of heavy metal ions in the environment are crucial due to their high toxicity and potential adverse effects on ecosystems and human health. Heavy metal ions, such as mercury (Hg 2+ ) [ 86 , 101 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 ], lead (Pb 2+ ) [ 67 , 98 , 106 , 116 , 117 , 118 , 119 ], chromium (Cr 6+ ) [ 120 , 121 , 122 , 123 ], copper (Cu 2+ ) [ 67 , 79 , 92 , 109 , 119 , 124 , 125 , 126 , 127 , 128 , 129 , 130 ], and silver (Ag + ) [ 78 , 117 , 131 , 132 , 133 ], can contaminate water, soil, and air through various industrial processes and human activities. Table 1 summarizes sensing of some heavy metal ions using CD-based ratiometric fluorescence probes.…”

Portable sensing methods based on carbon dots for food analysis

“…CDs synthesized by one‐pot solvothermal method mainly exist in solution. There are many ways to transfer CDs solution into solid form and stabilize them (Guo et al., 2018; Supchocksoonthorn et al., 2021). The easiest way is to combine CDs with a paper to prepare the test paper.…”

“…Test paper prepared using the same method was also used to detect Hg 2+ (Guo et al., 2018). Due to the fluorescence quenching of Hg 2+ on blue silicon nanocrystals, the fluorescence of R‐CDs that was not quenched by Hg 2+ in a mixed solution will gradually appear.…”