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The quenching of carbon dots (CDs) is affected by surface functional groups and other factors. Since CDs were also immobilized into thin films as a sensor, the effects of film properties on their photoluminescence should be investigated. In this work, N-doped CDs (NCDs) were immobilized in polyvinyl alcohol (PVA) thin films for tartrazine detection. Using a microwave-assisted hydrothermal method, amorphous NCDs were successfully produced. NCDs were blended into the PVA dope solution containing microfibrillated cellulose (MFC). An excessive amount of NCDs caused the undesired interaction and mutual reabsorption between the NCDs, resulting in self-quenching. Dimethylaminoethyl acrylate (DMAEMA) was added as copolymer to reduce the swelling ratio by about 50%. The reduction of water uptake subsequently reduced the tartrazine adsorption and the quenching of NCDs. Contradictory, the addition of TiO 2 nanoparticles improved the tartrazine adsorption and the NCDs quenching. The thin film also exhibits photocatalytic properties for analyte removal. The linear Δ F and the unchanged absorbance spectra of PVA/DM3/NCD/TiO 2 thin film indicate dynamic quenching at low tartrazine concentration (< 10 µM), attaining a limit of detection of 4.66 µM. The overlapping spectrum between the analyte absorbance and NCDs film emission spectra showed possible inner filter effects or fluorescence resonance energy transfer quenching mechanism. ga1 • N-doped carbon dots (NCDs) were immobilized in PVA thin film. • DMAEMA copolymerization reduced swelling and surface ratio of the PVA film. • TiO 2 nanoparticles improved tartrazine adsorption and quenching of NCDs. • Dynamic quenching occurred at low tartrazine concentration (<10 µM). • The photoluminescent intensity of the film was recovered after 4 h of UV cleaning. [ABSTRACT FROM AUTHOR]

Synthetic food colorant is commonly found in food products such as candies, beverages, pastry and dairy products. Excessive consumption of synthetic food colorant especially tartrazine may cause health problems. The discharge of wastewater containing tartrazine from food and beverage plants can further create environmental problems. Precise and rapid monitoring of food colorant during food and beverage processing at low cost is important to avoid these problems. A new class of fluorescent nanomaterials, carbon quantum dots (Cdots) with a size smaller than 10 nm have received great attention in the sensing of food colorant due to their biocompatibility, water solubility, low toxicity and excellent photostability. The dispersal of Cdots in solid-state thin films is important to further expand and reinforce their practical application. In this work, the dispersal of Cdots in low cost, biocompatible and transparent poly(vinyl alcohol) (PVA) and polyethylene glycol (PEG) was studied. Cdots were first synthesized via microwave assisted method before the dispersal in PVA and PVA/PEG solution. PVA/Cdots and PVA/PEG/Cdots thin films were formed using citric acid as the crosslinking agent and curing at 140 °C for 4 h. Cdots in spherical shapes with an average diameter smaller than 10 nm were successfully synthesized as proven in high resolution transmission electron microscopic (HRTEM) image. The effects of Cdots on thin film properties such as morphology and Fourier-transform infrared (FTIR) spectra were studied. The PL emission spectra of Cdots and PVA/PEG/Cdots thin film was recorded. The composite films showed photoluminescent property with the addition of Cdots. The films showed promising results to be developed as a tartrazine sensor in food quality control as they could detect tartrazine at a concentration as low as 10 μM. [ABSTRACT FROM AUTHOR]