Blue/red ratiometric pH sensors without background signals based on 808 nm-excited core–triple shell up-conversion nanoparticles

Abstract

A pH sensor based on CTS UCNPs exhibits ratiometric responses from pH 4 to 7 according to blue/red luminescence intensity ratios under 808 nm excitation.

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“…Often when variation in the upconversion spectral profile is induced (i.e., intensity or wavelength), at least one emission band remains unaffected and provides self-referencing for ratiometric detection (Figure 12A). 240,241 Alternatively, ratiometric luminescence sensing with upconverting RENPs can employ two emission wavelengths, each of which are excited with a different laser wavelength (Figure 12B). For example, the presence of an analyte can specifically induce the increase of one signal, followed by the decrease of the other, thereby establishing a substantial change in the ratio between these two detection signals.…”

“…247,248 Despite the benefits of significantly decreased heating, there is only a handful of publications on Nd 3+ -RENPs for pH sensing. 241 One of the most recent examples designed by T. Wang et al are NaGdF 4 :Yb 3+ ,Tm 3+ @ NaYF 4 :Yb 3+ ,Eu 3+ @NaYF 4 :Yb 3+ , Nd 3+ @NaYF 4 upconverting RENPs that were mixed with the pH indicator bromocresol green (BCG) to form pH sensor films. At ∼800 nm excitation, the red/blue (615 nm/450 nm) emission peak intensity ratio of RENPs was modulated by pH-sensitive BCG absorption to achieve a high sensitivity pH measurement in a value range of 4− 7.…”

“…Furthermore, as a result of Nd 3+ -sensitization, the employed excitation wavelength of ∼800 nm not only eliminated the impact of autofluorescence, but also allowed to alleviate the severe temperature rise in biological samples under continuous irradiation, ensuring accurate pH reading. 241 Another application of Nd 3+ -RENPs for ratiometric sensing was reported by H. Wang et al, who demonstrated efficient nitric oxide (NO) detection in cancer cells based on ratiometric luminescence imaging. The authors employed NaY-F 4 :Yb 3+ ,Er 3+ ,Nd 3+ @NaYF 4 :Nd 3+ core@shell upconverting RENPs that exhibited two independent emission wavelengths under ∼800 nm excitation.…”

“…In the ratiometric approach, two RENP emission bands are unevenly affected by surface interaction with the analyte, yielding improved sensitivity to the analyte and invariance to other environmental factors. Often when variation in the upconversion spectral profile is induced ( i.e ., intensity or wavelength), at least one emission band remains unaffected and provides self-referencing for ratiometric detection (Figure A). , …”

“…Owing to their effective elimination of background noise, upconverting RENPs-based pH sensing applications are commonly studied. , Despite the benefits of significantly decreased heating, there is only a handful of publications on Nd 3+ -RENPs for pH sensing . One of the most recent examples designed by T. Wang et al .…”