Sensitive detection of trace level Cd (II) triggered by chelation enhanced fluorescence (CHEF) “turn on”: Nitrogen-doped graphene quantum dots (N-GQDs) as fluorometric paper-based sensor

• Published in: Talanta (Oxford) 2022-05, Vol.242, p.123305-123305, Article 123305
• Main Authors: Naksen, Puttaraksa, Boonruang, Siwaluck, Yuenyong, Nunthawan, Lee, Hooi Ling, Ramachandran, Pravena, Anutrasakda, Wipark, Amatatongchai, Maliwan, Pencharee, Somkid, Jarujamrus, Purim
• Format: Article
• Language: English
• Subjects: Cadmium; Cadmium ion (Cd (II)); Chelation enhanced fluorescence (CHEF); Fluorescent sensor; Fluorometry; Graphite; Humans; Nitrogen; Nitrogen-doped graphene quantum dots (N-GQDs); Paper-based sensor; Quantum Dots
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2022.123305

Cadmium ion (Cd (II)) is a highly toxic heavy metal usually found in natural water. Exposure to Cd (II) can produce serious effects in human organs such as Itai-Itai disease. Therefore, the maximum allowance levels of Cd (II) in drinking water and herbal medicines imposed by the World Health Organization (WHO) are 3 μg L−1 and 300 μg kg−1, respectively. In this work, nitrogen-doped graphene quantum dots (N-GQDs) as a fluorescent sensor for Cd (II) determination was developed in both solution-based and paper-based systems. N-GQDs were synthesized from citric acid (CA) and ethylenediamine (EDA) via the hydrothermal method. The synthesized N-GQDs emitted intense blue fluorescence with a quantum yield (QY) of up to 80%. The functional groups on the surface of N-GQDs measured by FTIR were carboxyl (COO−), hydroxyl (OH−), and amine (NH2) groups, suggesting that they could be bound to Cd (II) for complexation. The fluorescence intensity of N-GQDs was gradually enhanced with the increase of Cd (II) concentration. This phenomenon was proved to result from the fluorescence enhancement (turn-on) based on the chelation enhanced fluorescence (CHEF) mechanism. Under the optimum conditions in the solution-based and paper-based systems, the limits of detection (LODs) were found to be 1.09 and 0.59 μg L−1, respectively. Furthermore, the developed sensors showed relatively high selectivity toward Cd (II) over ten other metal cations and six other anions of different charges. The performance of the sensor in real water and herbal medicine samples exhibited no significant difference as compared to the results of the validation method (ICP-OES). Therefore, the developed sensors can be used as fluorescent sensors for Cd (II) determination with high sensitivity, high selectivity, short incubation time (5 min). As such, the paper-based strategy has excellent promising potential for practical analysis of Cd (II) in water and herbal medicine samples with a trace level of Cd (II) concentrations. [Display omitted] •Novel paper-based N-GQDs sensor for trace-level probing of Cd (II) was developed.•User-friendly probing involved chelation enhanced fluorescence (turn-on) mechanism.•Sensor had high selectivity toward Cd (II) over 16 other metal cations and anions.•Sensor offers simple fabrication, high sensitivity, and short incubation time.•Sensor was validated by ICP-OES and applicable for real water and medicine samples.