Topics in Current Chemistry (2020) 378:28
1 3
synthesized for an ECL immunoassay of N-terminal brain natriuretic peptide. The
band levels of TiO 2 and g-C 3 N 4 are well matched, increasing the ECL emission
efficiency. Polydopamine (PDA) linked with Ab 2 was employed as a ECL quencher
to improve detection sensitivity. Wei’s group [39] reported an ECL immunosensor
for CEA based on the composite Au-FrGO-CeO 2 @TiO 2 , where Au-FrGO refers
to Fe 3 O 4 capped with reduced graphene oxide functionalized with Au NPs. When
K 2 S 2 O 8 was employed as a coreactant, CeO 2 @TiO 2 was found to yield greater ECL
intensity than TiO 2 . The resulting CeO 2 @TiO 2 heterojunction presented a smaller
band gap than TiO 2 , facilitating electron transfer between the CeO 2 @TiO 2 composite and its coreactant. The Au-FrGO was included to further amplify the ECL signal.
When tested, the ECL biosensor displayed a sensitive response to CEA. Tian et al.
[40] presented an ECL immunosensor based on TiO 2 nanotube arrays functionalized with graphene quantum dots (GQDs). Vertically aligned TiO 2 nanotubes were
included to provide a large surface area on which to immobilize the GQDs and antibody. The ECL intensity was enhanced sixfold after immobilizing the GQDs to form
a hybrid structure (GQD/TiO 2 NTs). Under optimized conditions, PSA was sensitively detected using CdTe NPs modified with Fe 3 O 4 magnetic nanoparticles (CdTe/
MNPs) as a quenching label. Cui and coauthors [41] developed a potential-resolved
ECL strategy for the label-free ratiometric aptasensing of cTnI that involved wrapping titanium dioxide in nanographene oxide (nGO@TiO 2 NLPs) employing a
“one-pot” hydrothermal method (Fig. 5a). Using K 2 S 2 O 8 as a coreactant, as shown
in Fig. 5b, this nanocomposite yielded dual ECL emission (ECL-1 and ECL-2) at
− 1.27 V and − 1.85 V, respectively (black line). In contrast, TiO 2 (green line) and
nGO (blue line) each provided just one ECL emission peak under the same conditions. ECL-1 and ECL-2 were found to correspond with the ECL emissions of
TiO 2 and nGO by comparing ECL potentials and emission wavelengths (Fig. 5b–d),
but the intensities of ECL-1 and ECL-2 were observed to be considerably stronger
than the corresponding ECL emission intensities of TiO 2 and nGO alone due to
a synergistic effect. After capturing the target, the aptamer moved away from the
electrode surface because of its rigidity, reducing the resistance of the electrode and
enhancing the two ECL signals from the nGO@TiO 2 NLPs. Furthermore, the intensity of ECL-1 and the ECL intensity of TiO 2 were observed to increase in an oxygen
atmosphere and to decrease in a nitrogen atmosphere because some of the O 2 was
electroreduced and subsequently reacted with S 2 O 8
2−
to generate SO 4
•−
. Similarly,
Dai et al. [42] proposed a simple dual coreactant strategy to enhance the ECL performance of TiO 2 nanotubes. When K 2 S 2 O 8 and H 2 O 2 were added simultaneously,
the ECL intensity of TiO 2 increased 6.3-fold and 107-fold, respectively, compared to
when only K 2 S 2 O 8 or H 2 O 2 was added as a coreactant, which was attributed to the
increased concentration of SO 4
•−
caused by the presence of H 2 O 2 on the electrode
surface. This mechanistic study of the ECL enhancement caused by dual coreactants
could provide a general strategy for improving ECL-based applications of semiconductor nanomaterials.
Besides acting as an immobilization substrate, TiO 2 catalyzes the oxidation of H 2 O 2 , which makes TiO 2 suitable for fabricating biofunctional ECL
electrodes. Wu et al. [43] reported an enzymatic ECL choline sensor based on
a Fe 3 O 4 -TiO 2 -choline oxidase (ChO) biocomposite. Choline was oxidized with
10
Reprinted from the journal
1 3
synthesized for an ECL immunoassay of N-terminal brain natriuretic peptide. The
band levels of TiO 2 and g-C 3 N 4 are well matched, increasing the ECL emission
efficiency. Polydopamine (PDA) linked with Ab 2 was employed as a ECL quencher
to improve detection sensitivity. Wei’s group [39] reported an ECL immunosensor
for CEA based on the composite Au-FrGO-CeO 2 @TiO 2 , where Au-FrGO refers
to Fe 3 O 4 capped with reduced graphene oxide functionalized with Au NPs. When
K 2 S 2 O 8 was employed as a coreactant, CeO 2 @TiO 2 was found to yield greater ECL
intensity than TiO 2 . The resulting CeO 2 @TiO 2 heterojunction presented a smaller
band gap than TiO 2 , facilitating electron transfer between the CeO 2 @TiO 2 composite and its coreactant. The Au-FrGO was included to further amplify the ECL signal.
When tested, the ECL biosensor displayed a sensitive response to CEA. Tian et al.
[40] presented an ECL immunosensor based on TiO 2 nanotube arrays functionalized with graphene quantum dots (GQDs). Vertically aligned TiO 2 nanotubes were
included to provide a large surface area on which to immobilize the GQDs and antibody. The ECL intensity was enhanced sixfold after immobilizing the GQDs to form
a hybrid structure (GQD/TiO 2 NTs). Under optimized conditions, PSA was sensitively detected using CdTe NPs modified with Fe 3 O 4 magnetic nanoparticles (CdTe/
MNPs) as a quenching label. Cui and coauthors [41] developed a potential-resolved
ECL strategy for the label-free ratiometric aptasensing of cTnI that involved wrapping titanium dioxide in nanographene oxide (nGO@TiO 2 NLPs) employing a
“one-pot” hydrothermal method (Fig. 5a). Using K 2 S 2 O 8 as a coreactant, as shown
in Fig. 5b, this nanocomposite yielded dual ECL emission (ECL-1 and ECL-2) at
− 1.27 V and − 1.85 V, respectively (black line). In contrast, TiO 2 (green line) and
nGO (blue line) each provided just one ECL emission peak under the same conditions. ECL-1 and ECL-2 were found to correspond with the ECL emissions of
TiO 2 and nGO by comparing ECL potentials and emission wavelengths (Fig. 5b–d),
but the intensities of ECL-1 and ECL-2 were observed to be considerably stronger
than the corresponding ECL emission intensities of TiO 2 and nGO alone due to
a synergistic effect. After capturing the target, the aptamer moved away from the
electrode surface because of its rigidity, reducing the resistance of the electrode and
enhancing the two ECL signals from the nGO@TiO 2 NLPs. Furthermore, the intensity of ECL-1 and the ECL intensity of TiO 2 were observed to increase in an oxygen
atmosphere and to decrease in a nitrogen atmosphere because some of the O 2 was
electroreduced and subsequently reacted with S 2 O 8
2−
to generate SO 4
•−
. Similarly,
Dai et al. [42] proposed a simple dual coreactant strategy to enhance the ECL performance of TiO 2 nanotubes. When K 2 S 2 O 8 and H 2 O 2 were added simultaneously,
the ECL intensity of TiO 2 increased 6.3-fold and 107-fold, respectively, compared to
when only K 2 S 2 O 8 or H 2 O 2 was added as a coreactant, which was attributed to the
increased concentration of SO 4
•−
caused by the presence of H 2 O 2 on the electrode
surface. This mechanistic study of the ECL enhancement caused by dual coreactants
could provide a general strategy for improving ECL-based applications of semiconductor nanomaterials.
Besides acting as an immobilization substrate, TiO 2 catalyzes the oxidation of H 2 O 2 , which makes TiO 2 suitable for fabricating biofunctional ECL
electrodes. Wu et al. [43] reported an enzymatic ECL choline sensor based on
a Fe 3 O 4 -TiO 2 -choline oxidase (ChO) biocomposite. Choline was oxidized with
10
Reprinted from the journal