1 3
Topics in Current Chemistry (2020) 378:28
strongly catalytic properties, the TiO 2 NFs promoted the reduction of dissolved O 2
to yield OH
•
radicals, which reacted with the Ag NCs, leading to stronger ECL
emission (Fig. 6c). Ferrocene-labeled DNA was employed as an ECL quenching
probe to further improve the sensitivity of the proposed biosensor. The catalysis of
the reduction of dissolved O 2 by TiO 2 has also been applied to enhance the cathodic
ECL intensity of Au 25 NCs in a sensitive ECL biosensor [49]. Oxygen vacancies
of TiO 2 could improve the electrocatalytic performance [50]. And using X-ray photoelectron spectroscopy, Liang et al. [51] discovered that oxygen vacancies in Cudoped TiO 2 NPs could act as reactive centers for the conversion of dissolved O 2
into superoxide radicals (O 2
•−
), which intensified the ECL of luminol. In another
study, S 2 O 8
2−
was employed as a coreactant and TiO 2 as its accelerator [52] in
order to enhance the ECL efficiency of the Cu NCs used in an ultrasensitive ECL
biosensor for microRNA detection. In the presence of the target, a cascade leading to signal amplification and a hybridization chain reaction were triggered, causing AT-rich double-stranded DNA to be generated on the TiO 2 . The Cu NCs that
acted as the ECL luminophore in this detection system were then generated in situ
on the dsDNA via A–Cu
2+
–T bonding. The TiO 2 not only provided a platform for
the dsDNA functionalized with Cu NCs, but it also helped to generate SO 4
•−
, which
improved the performance of the ECL biosensor. Zhang et al. [16] prepared a ternary ECL biosensor based on Ru(bpy) 2 (cpaphen)
2+
/TPrA/TiO 2 nanoneedles for the
detection of glutathione. The electrode was modified with TiO 2 nanoneedles in
order to immobilize long dsDNA structures that adsorbed Ru(bpy) 2 (cpaphen)
2+
, the
ECL luminophor. The TiO 2 nanoneedles also acted as an accelerator for the oxidation of tripropylamine (TPrA), significantly intensifying the ECL signal from
Ru(bpy) 2 (cpaphen)
2+
. When a voltage was applied to the system, electrons tunneled from the VB of TiO 2 to the CB. The holes generated in the VB were filled
by electrons from TPrA, generating TPrA
+•
. Finally, GSH recognition was achieved
with this system by including MnO 2 nanosheets, which were reduced by the GSH to
Mn
2+
; and then Mn
2+
worked as cofactor to cleave the Ru-dsDNA structures.
4 Conclusion and Future Perspectives
This review has focused on the development of novel TiO 2 -based nanomaterials and
innovative applications of them in PEC and ECL biosensing. Such biosensors based
on TiO 2 nanomaterials are particularly interesting mechanistically and from the perspective of biosensing applications due to the special photoelectric interconversion
processes they use to probe biorecognition and biocatalytic events. However, there
are still several challenges in the practical application of TiO 2 nanomaterials to PEC
and ECL biosensing. First, TiO 2 nanomaterials have relatively low PEC and ECL
efficiencies, so other nanomaterials such as QDs or noble metal NPs are usually
incorporated into the biosensing system to optimize its performance. In many cases,
the strategies used to synthesize the TiO 2 -based nanomaterials have been taken
directly from energy and photocatalysis research, and the resulting nanomaterials
may be not suitable for use in bioassays. More effort should be directed into designing TiO 2 nanomaterials that are specifically for PEC and ECL biosensing. Second,
13
Reprinted from the journal
Topics in Current Chemistry (2020) 378:28
strongly catalytic properties, the TiO 2 NFs promoted the reduction of dissolved O 2
to yield OH
•
radicals, which reacted with the Ag NCs, leading to stronger ECL
emission (Fig. 6c). Ferrocene-labeled DNA was employed as an ECL quenching
probe to further improve the sensitivity of the proposed biosensor. The catalysis of
the reduction of dissolved O 2 by TiO 2 has also been applied to enhance the cathodic
ECL intensity of Au 25 NCs in a sensitive ECL biosensor [49]. Oxygen vacancies
of TiO 2 could improve the electrocatalytic performance [50]. And using X-ray photoelectron spectroscopy, Liang et al. [51] discovered that oxygen vacancies in Cudoped TiO 2 NPs could act as reactive centers for the conversion of dissolved O 2
into superoxide radicals (O 2
•−
), which intensified the ECL of luminol. In another
study, S 2 O 8
2−
was employed as a coreactant and TiO 2 as its accelerator [52] in
order to enhance the ECL efficiency of the Cu NCs used in an ultrasensitive ECL
biosensor for microRNA detection. In the presence of the target, a cascade leading to signal amplification and a hybridization chain reaction were triggered, causing AT-rich double-stranded DNA to be generated on the TiO 2 . The Cu NCs that
acted as the ECL luminophore in this detection system were then generated in situ
on the dsDNA via A–Cu
2+
–T bonding. The TiO 2 not only provided a platform for
the dsDNA functionalized with Cu NCs, but it also helped to generate SO 4
•−
, which
improved the performance of the ECL biosensor. Zhang et al. [16] prepared a ternary ECL biosensor based on Ru(bpy) 2 (cpaphen)
2+
/TPrA/TiO 2 nanoneedles for the
detection of glutathione. The electrode was modified with TiO 2 nanoneedles in
order to immobilize long dsDNA structures that adsorbed Ru(bpy) 2 (cpaphen)
2+
, the
ECL luminophor. The TiO 2 nanoneedles also acted as an accelerator for the oxidation of tripropylamine (TPrA), significantly intensifying the ECL signal from
Ru(bpy) 2 (cpaphen)
2+
. When a voltage was applied to the system, electrons tunneled from the VB of TiO 2 to the CB. The holes generated in the VB were filled
by electrons from TPrA, generating TPrA
+•
. Finally, GSH recognition was achieved
with this system by including MnO 2 nanosheets, which were reduced by the GSH to
Mn
2+
; and then Mn
2+
worked as cofactor to cleave the Ru-dsDNA structures.
4 Conclusion and Future Perspectives
This review has focused on the development of novel TiO 2 -based nanomaterials and
innovative applications of them in PEC and ECL biosensing. Such biosensors based
on TiO 2 nanomaterials are particularly interesting mechanistically and from the perspective of biosensing applications due to the special photoelectric interconversion
processes they use to probe biorecognition and biocatalytic events. However, there
are still several challenges in the practical application of TiO 2 nanomaterials to PEC
and ECL biosensing. First, TiO 2 nanomaterials have relatively low PEC and ECL
efficiencies, so other nanomaterials such as QDs or noble metal NPs are usually
incorporated into the biosensing system to optimize its performance. In many cases,
the strategies used to synthesize the TiO 2 -based nanomaterials have been taken
directly from energy and photocatalysis research, and the resulting nanomaterials
may be not suitable for use in bioassays. More effort should be directed into designing TiO 2 nanomaterials that are specifically for PEC and ECL biosensing. Second,
13
Reprinted from the journal