A ratiometric optical sensor has been developed with electrospinning processing method for dissolved oxygen measurement. The sensing film is fabricated by using silver nano-particles (Ag NPs) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride complex (Ru(DPP)₃Cl₂) encapsulated in plasticized polymethyl methacrylate (PMMA). An insensitive 3-(2-benzothiazolyl)-7-(diethy lamino)-(6CI,7CI) (Coumarin6) is adopted as reference. The ratio of oxygenation is calculated at each image pixel of a 3CCD camera to quantify the oxygen concentration in aqueous environment. Compared to Ag-free film, the response time of Ag-containing films were improved from 1.5 s to 1.0 s upon switching from deoxygenated to air saturation and from 65 s to 45 s from air saturation to fully deoxygenated. The response times of the Ag-free film obtained by knifing was 2.0 s upon switching from deoxygenated to air saturation and 104 s from air saturation to fully deoxygenated. Results of the evaluation of accuracy, limit of detection, stability, and photostability are presented. An experiment measuring the spatiotemporal variation of oxygen distribution within the photosynthesis and respiration of Chlorella vulgaris is demonstrated. It is shown that the nanofiber-based optical sensor film could serve as a promising method for rapid oxygen monitoring in aqueous applications.

This paper presents a simple, high resolution imaging approach utilizing ratiometric planar optode for simultaneous measurement of dissolved oxygen (DO) and pH. The planar optode comprises a plastic optical film coated with oxygen indicator Platinum(II) octaethylporphyrin (PtOEP) and reference quantum dots (QDs) embedded in polystyrene (PS), pH indicator 5-Hexadecanoylamino-fluorescein (5-Fluorescein) embedded in Hydromed D4 matrix. The indicator and reference dyes are excited by utilizing an LED (Light Emitting Diode) source with a central wavelength of 405 nm, the emission respectively matches the different channels (red, green, and blue) of a 3CCD camera after eliminating the excitation source by utilizing the color filter. The result shows that there is low cross-sensitivity between the two analytes dissolved oxygen and pH, and it shows good performance in the dynamic response ranges of 0–12 mg/L and a dynamic range of pH 6−8. The optode has been tested with regard to the response times, accuracy, photostability and stability. The applied experiment for detecting pH/Oxygen of sea-water under the influence of the rain drops is demonstrated. It is shown that the planar optode measuring system provides a simple method with low cross-talk for pH/Oxygen imaging in aqueous applications.

PH sensors based on up-conversion nanoparticles (UCNPs) are widely studied due to their effective elimination of background signals. However, ratiometric pH measurement depending on blue and red luminescence under NIR irradiation has been seldom reported for the lack of simultaneous strong blue and red emissions for traditional UCNPs. In this work, we designed NaGdF₄:Yb,Tm@NaYF₄:Yb,Eu@NaYF₄:Yb,Nd@NaYF₄ core–triple shell (CTS) UCNPs as fluorescent materials to realize blue/red ratiometric pH measurement. On the basis of Gd³⁺-mediated interfacial energy transfer and Yb³⁺-mediated energy migration, CTS particles present intense luminescence and a high red/blue (615 nm/450 nm) peak intensity ratio of 0.47 at 808 nm excitation. Composed of these particles and pH indicator bromocresol green, the pH sensor exhibits ratiometric responses in a pH range of 4–7 according to blue/red luminescence intensity ratios, avoiding the common errors as well as potential mutual fluorescence signal interference. Owing to strong overall luminescence and additional red emission of CTS UCNPs distinctly improving the signal-to-noise ratio, this ratiometric sensor reveals high sensitivity. Moreover, the employed excitation wavelength of 808 nm can not only eliminate autofluorescence signals, but also alleviate severe temperature rise in biosamples under continuous irradiation, ensuring accurate pH determination. More intriguingly, a CCD RGB camera serves as a collector to record luminescence signals, further promoting commercial feasibility. The successful application of CTS UCNPs on sensors indeed realizes blue/red ratiometric measurement towards pH under 808 nm irradiation, also pointing out a novel way for pH sensors with high sensitivity and accuracy.

The sensing mechanism toward Hcy/Cys is realized based on the condensation reaction, which breaks CN to form a thiazolidine adduct.