The application of fluorescent carbon nanodots (C-dots or CD), non-toxic particulate organic labels, to disease biomarker detection is still in its earliest stage of development. In the effort described here, a novel ratiometric immunoassay was developed to target a model protein disease biomarker, alpha-fetoprotein (AFP), using C-dot doped silica nanoparticles (CD-SNPs) and fluorescein isothiocyanate (FITC) as signaling agents. Highly fluorescent C-dots were hydrothermally synthesized from citric acid and ethylene diamine. The C-dots were then encapsulated in silicate shells to yield 45 nm nanoparticles using a novel reverse microemulsion method, enabling convenient handling (centrifugation and washing) and straightforward surface chemistry modification to facilitate development of bioassays. Capture antibody capped CD-SNPs (Ab₁-CD-SNPs), together with FITC labeled antibodies (Ab₂-FITC) constituted a new ratiometric immunosensor for AFP, in which CD-SNPs functioned as both solid supports for washing and separation and as built-in reference signaling agents to correct for inconsistent environmental effects. A calibration curve was established between the ratiometric signal (the ratio of fluorescence signals of FITC and C-dots, F/C) and AFP concentration in the broad range of 0.317–280 μg dL⁻¹, exhibiting a useful linear range (0.317–35 μg dL⁻¹, R² = 0.9977), low detection limit (0.317 μg dL⁻¹) and acceptable recovery (105–120%). This assay format can be applied to a wide range of immunoassay targets. Our demonstration of encapsulating low-cost, easily synthesized, highly-fluorescent C-dots into silica nanoparticles for use in immunoassays will be useful in expanding future applications of these carbon nanomaterials to areas such as in vivo cellular imaging, drug delivery, and in vitro cell labeling and biomolecule sensing.

The objective of this study was to investigate the relationship of acute pesticide exposures and acute changes in thyroid hormones among Thai farmers. We recruited 78 farmers, who were scheduled to spray insecticides (chlorpyrifos and/or cypermethrin) or herbicides (paraquat and/or glyphosate). On the day before spraying, farmers collected their first morning void urine and went for blood collection. On the spray day, urine samples were collected at end of the spraying event and they were interviewed with questionnaires. The next morning, the first morning void urine and blood samples were collected. Blood samples were analyzed for thyroid hormones. Urine samples were analyzed for the metabolites of the pesticide sprayed. The results showed that the thyroid hormones, free triiodothyronine (FT3) and total triiodothyronine (T3) were significantly reduced as urinary chlorpyrifos metabolite increased the day after spraying. Total thyroxine (T4) significantly increased as cypermethrin metabolites increased the day after spraying. T4 significantly increased as urinary glyphosate levels increased; however, FT3 and T3 decreased significantly as urinary paraquat levels increased the day after spraying. These findings suggest that acute exposures to the pesticides chlorpyrifos, cypermethrin, paraquat and glyphosate can produce acute effects on the hypothalamic–pituitary–thyroid (HPT) axis, acutely altering thyroid hormone levels.

A detection method for type-II pyrethroids in an environmental water sample using a microfluidic paper-based analytical device (µPAD) is reported here. The detection approach is based on the formation of cyanide from the hydrolysis of type-II pyrethroids and the colorimetric detection of cyanide on a layer-based µPAD. Parafilm and inexpensive laminating pouches were used to create a hydrophobic barrier for the assay on the µPAD. This detection approach was selective to type-II pyrethroids in water for which an environmental water sample was tested. The calibration curves for cypermethrin, deltamethrin, cyhalothrin, and fenvalerate ranged from 2 to 40 µg/mL without sample preconcentration. The lower concentrations of type-II pyrethroids can be assessed by including a preconcentration step prior to the detection on a µPAD. This detection system provides an alternative platform for fast, semiquantitative testing for pesticide contamination in environmental surface water by allowing for portability, low reagent/sample consumption, and low-cost testing.