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Study on photophysical and aggregation induced emission recognition of 1,8-naphthalimide probe for casein by
Yang Sun1, Zhen Liu, Xuhua Liang
1Department of Chemistry & Chemical Engineering, Xi'an University of Arts and Science, No. 168 Taibai South Road, Xi'an, Shaanxi 710065, China. 66160692@qq.com
Insights
A novel fluorescent probe utilizing aggregation-induced emission (AIE) enables sensitive detection of casein. This method offers a reliable and rapid assay for casein quantification in milk powder.
Area of Science:
- Analytical Chemistry
- Materials Science
- Biochemistry
Background:
- Developing sensitive and selective fluorescent probes is crucial for biomolecule detection.
- 1,8-naphthalimide derivatives are known for their photophysical properties and potential in sensing applications.
- Aggregation-Induced Emission (AIE) is a phenomenon that enhances fluorescence upon aggregation, useful for developing turn-on probes.
Purpose of the Study:
- To design and synthesize a novel water-soluble 1,8-naphthalimide derivative for casein detection.
- To investigate the photophysical properties and sensing mechanism of the naphthalimide derivative.
- To develop a rapid and sensitive assay for casein quantification.
Main Methods:
- Synthesis of a water-soluble 1,8-naphthalimide derivative with two acetic carboxylic groups.
- Photophysical characterization in various solvents to understand emission mechanisms (TICT, self-association).
- Density Functional Theory (DFT) calculations to elucidate electronic properties.
- Casein detection assay development utilizing the AIE characteristics of the probe.
Main Results:
- The naphthalimide derivative exhibited fluorescent turn-on recognition for casein via AIE.
- The probe showed solvent-dependent fluorescence, with decreased intensity in polar solvents due to TICT and hydrogen bonding.
- DFT calculations confirmed strong TICT character.
- The AIE mechanism with casein involved docking into hydrophobic cavities and binding with Tyr and Trp residues, leading to aggregation and enhanced emission.
- A casein assay was developed with a linear range of 0.1–22 μg mL⁻¹, a detection limit of 2.8 ng mL⁻¹, and good reproducibility and reversibility.
- The method successfully determined casein in milk powder samples.
Conclusions:
- A novel AIE-active 1,8-naphthalimide derivative was successfully synthesized and characterized.
- The developed fluorescent probe provides a sensitive and selective method for casein detection.
- The assay is suitable for practical application in analyzing casein content in food products like milk powder.
Abstract:
A novel water-soluble 1,8-naphthalimide derivative 1, bearing two acetic carboxylic groups, exhibited fluorescent turn-on recognition for casein based on the aggregation induced emission (AIE) character. The photophysical properties of 1 consisting of donor and acceptor units were investigated in different solutions. The fluorescence intensity decreased through taking advantage of twisted intramolecular charge transfer (TICT) and self-association emission with increasing solvent polarity. Moreover, the spectral red-shift and intensity quench in protic solvents were caused by the excited-state hydrogen bond strengthening effect. Density Functional Theory (DFT) calculations revealed that 1 exhibited a strong TICT character. The AIE mechanism of 1 with casein was due to 1 docked in the hydrophobic cavity between sub-micelles and bound with Tyr and Trp residues, resulting in the aggregation of 1 on the casein surface and emission enhancement. Based on this, a novel casein assay method was developed. The proposed exhibited a good linear range from 0.1 to 22 μg mL(-1), with the detection limit of 2.8 ng mL(-1). Satisfactory reproducibility, reversibility and a short response time were realized. This method was applied to the determination of casein in milk powder samples and the results were in good agreement with the result of Biuret method.
