Table 1
pH sensors based on upconversion nanohybrids (UCNHs)
n.
Cooperative species
UCNP
UCNH size
(nm)
pH linear
response
Detection
Year Ref.
Case (i) Inner-filter mechanism
1.
Bromothymol blue
NaYF
4 :Yb,Er
50
 950
6–10
I
658 (Er)
2009 [55]
2.
Phenol red
NaYF
4 :Yb,Er
60–90
6–8
I
541 (Er)/I
655 (Er)
2010 [44]
3.
Polyglutamic porphyrin
dendrimers
β-NaYF 4 :Yb, Er
23
6–9
I
520–540 (Er)/I
660 (Er)
2012 [56]
4.
ETH 5418
β-NaYF 4 :Yb,Er
200
 1,000
6–11
I
656 (Er)/I
542 (Er)
2012 [57]
5.
Bromocresol green
Y
2 O
2 S:Yb,Er
200–300
5–10
I
671 (Er)/I
661 (Er)
2014 [58]
6.
Neutral red
Gd
2 O
2 S:Yb,Er
1,500
6–8
I
520–540 (Er)/I
650 (Er)
2014 [59]
7.
Bromothymol blue
NaGdF
4 :Yb,Er
200
 1,200
6–8
I
650–700 (Er)
2014 [60]
8.
Bromocresol green +
bromothymol blue
α-NaYF 4 :Yb,Mn,Eu
@α-NaYF
4 @PEG
24
3–8
I
592 + 609 (Eu)/I
700 (Eu)
2014 [61]
9.
Aza-BODIPY dimethylamino
NaCaY
0.2 Yb
0.7 Tm
0.02 Ho
0.08 (MoO
4 )
3
Bulk
7–10
I
797 (Tm)/I
645 (Ho)
2016 [36]
10. Bromothymol blue
Rhodamine B
β-NaYF 4 :Yb,Er@SiO
2 @BSA
240
6–8
5–6.5
I
540 (Er)/I
655 (Er)
I
550 (Er)/I
655 (Er)
2017 [62]
11. Bromophenol-BODIPY
derivatives
β-NaYF 4 :Yb,Tm@PEI
27
5–7
7–9
A
500–600 (dye)/A
630–
675 (Tm)
2019 [38]
Case (ii) LRET and dye resonant emission play a role in the sensor response
12. pHrodo red™
β-NaYF 4 :Yb,Er@SiO
2
28
 36
3–6.7
I
590 (dye)/I
550 (Er)
2014 [63]
13. pHrodo red™
β-NaYF 4 :Yb,Er@PEI
23
 27
3–7
I
590 (dye)/I
550 (Er)
2016 [49]
14. Fluorescein isothiocyanate
β-NaYF 4 :Yb,Tm@SiO
2
23
4–10
I
519 (dye)/I
465 (Tm)
2016 [48]
15. Fluorescein
β-NaGdF 4 :Yb,Tm
@β-NaGdF
4 :Nd,Yb@β-NaYF
4
22
5–8
I
515 (dye)/I
645 (Tm)
2017 [50]
16. Hemicyanine derivative
β-NaGdF 4 @β-NaYF
4 :Yb,Tm
@β-NaYF
4 @PAA
30
6.8–9
I
650 (Tm)/I
513 (dye)
2017 [64]
17. GM-Ag
2 S nanodots
α-NaGdF 4 :Yb,Tm@SiO
2
70
4–9
I
795 (GM-Ag
2 S)/
I
540 (Er)
2019 [52]
382
J. Ferrera-González et al.