Topics in Current Chemistry (2020) 378:28
1 3
numerous functional groups at which to immobilize antibodies (Ab 1 ) for cTnI (cardiac troponin I). In another study, mesoporous TiO 2 functionalized with CdS QDs
(acting as a sensitizer) was synthesized to facilitate enhanced PEC aptasensing of
PSA (prostate-specific antigen) [24]. Ordered mesoporous TiO 2 is an ideal platform
for incorporating CdS QDs due to its multiple scattering properties and large surface
area. The combination of QDs and mesoporous TiO 2 was found to promote charge
transfer and electron–hole pair separation at the interface. Recently, graphite-like
carbon nitride (g-C 3 N 4 ) QDs and N-doped graphene QDs (N-GQDs) [10] were used
to sensitize TiO 2 nanopillars and therefore achieve stronger visible light absorbance
for the sensitive PEC detection of pcDNA3-HBV (hepatitis B virus). The band gaps
of the TiO 2 , the g-C 3 N 4 QDs, and the N-GQDs were 3.2, 2.76, and 1.7 eV, respectively. After incorporating the g-C 3 N 4 and N-GQDs, the charge transfer and electron–hole separation efficiency improved considerably due to photosensitization and
the formation of a heterojunction between g-C 3 N 4 and TiO 2 .
The utilization of a heterostructure comprising TiO 2 and a semiconductor with
a suitable band gap and matched energy levels can tremendously decrease charge
recombination, enhance the electron transfer efficiency, and increase light absorption in PEC biosensors. Liu et al. [13] presented a PEC biosensing strategy based
on a heterostructure containing MoS 2 nanosheets and TiO 2 nanorods. The TiO 2
nanorods served as hydrothermal growth templates for the MoS 2 nanosheets, which
were a few layers thick. The band edge of the MoS 2 nanosheets was well matched
to that of TiO 2 , facilitating the separation and transfer of the photogenerated charge.
Due to the excellent biocompatibility of this system, glucose oxidase (GOx) was
immobilized onto a MoS 2 /TiO 2 nanocomposite-modified ITO electrode for the sensitive detection of glucose under visible light irradiation. In addition, a TiO 2 –BiVO 4
heterostructure [21] for PEC biosensing has been obtained by depositing BiVO 4
NPs onto TiO 2 nanospheres using a solvothermal method. The narrow energy gap
(2.34 eV) of BiVO 4 was found to improve the absorption of the heterostructure in
the visible light region. The high surface area and biocompatible microenvironment of the TiO 2 –BiVO 4 heterostructure permitted improved loading of recognition biomolecules for 17β-estradiol measurements. Also, as shown in Fig. 1b, a
heterojunction consisting of MgIn 2 S 4 nanoplates and a TiO 2 nanoarray was developed [11] for the PEC aptasensing of adenosine triphosphate (ATP). Interestingly,
the TiO 2 nanoarray was observed to have better photoelectric properties than TiO 2
NPs, including a narrower bandgap (~ 3.0 eV), higher conductivity, and reduced
recombination of electron–hole pairs. The presence of the MgIn 2 S 4 /TiO 2 nanoarray
heterojunction improved visible light absorption, resulting in a ~ 6.8-fold increase
in photocurrent compared with a more conventional TiO 2 electrode. Ferrocene, an
electron donor employed as a label, has been used to accelerate electron–hole separation and thus enhance the photocurrent in PEC biosensors. In particular, Wei’s
group [15] reported the cytosensing of RAW264.7 macrophage cells utilizing a TiO 2
nanoneedles@MoO 3 array p–n heterojunction. MoO 3 is a p-type semiconductor
with a relatively wide band gap of 2.9 eV; its absorption peak is near to the UV light
region. Coupling MoO 3 with TiO 2 yielded a p–n heterojunction that promoted visible light absorption due to the offset of 2.61 eV between the valence band (VB) of
TiO 2 and the conduction band (CB) of MoO 3 . Immobilizing F4/80 antibodies used
4
Reprinted from the journal
1 3
numerous functional groups at which to immobilize antibodies (Ab 1 ) for cTnI (cardiac troponin I). In another study, mesoporous TiO 2 functionalized with CdS QDs
(acting as a sensitizer) was synthesized to facilitate enhanced PEC aptasensing of
PSA (prostate-specific antigen) [24]. Ordered mesoporous TiO 2 is an ideal platform
for incorporating CdS QDs due to its multiple scattering properties and large surface
area. The combination of QDs and mesoporous TiO 2 was found to promote charge
transfer and electron–hole pair separation at the interface. Recently, graphite-like
carbon nitride (g-C 3 N 4 ) QDs and N-doped graphene QDs (N-GQDs) [10] were used
to sensitize TiO 2 nanopillars and therefore achieve stronger visible light absorbance
for the sensitive PEC detection of pcDNA3-HBV (hepatitis B virus). The band gaps
of the TiO 2 , the g-C 3 N 4 QDs, and the N-GQDs were 3.2, 2.76, and 1.7 eV, respectively. After incorporating the g-C 3 N 4 and N-GQDs, the charge transfer and electron–hole separation efficiency improved considerably due to photosensitization and
the formation of a heterojunction between g-C 3 N 4 and TiO 2 .
The utilization of a heterostructure comprising TiO 2 and a semiconductor with
a suitable band gap and matched energy levels can tremendously decrease charge
recombination, enhance the electron transfer efficiency, and increase light absorption in PEC biosensors. Liu et al. [13] presented a PEC biosensing strategy based
on a heterostructure containing MoS 2 nanosheets and TiO 2 nanorods. The TiO 2
nanorods served as hydrothermal growth templates for the MoS 2 nanosheets, which
were a few layers thick. The band edge of the MoS 2 nanosheets was well matched
to that of TiO 2 , facilitating the separation and transfer of the photogenerated charge.
Due to the excellent biocompatibility of this system, glucose oxidase (GOx) was
immobilized onto a MoS 2 /TiO 2 nanocomposite-modified ITO electrode for the sensitive detection of glucose under visible light irradiation. In addition, a TiO 2 –BiVO 4
heterostructure [21] for PEC biosensing has been obtained by depositing BiVO 4
NPs onto TiO 2 nanospheres using a solvothermal method. The narrow energy gap
(2.34 eV) of BiVO 4 was found to improve the absorption of the heterostructure in
the visible light region. The high surface area and biocompatible microenvironment of the TiO 2 –BiVO 4 heterostructure permitted improved loading of recognition biomolecules for 17β-estradiol measurements. Also, as shown in Fig. 1b, a
heterojunction consisting of MgIn 2 S 4 nanoplates and a TiO 2 nanoarray was developed [11] for the PEC aptasensing of adenosine triphosphate (ATP). Interestingly,
the TiO 2 nanoarray was observed to have better photoelectric properties than TiO 2
NPs, including a narrower bandgap (~ 3.0 eV), higher conductivity, and reduced
recombination of electron–hole pairs. The presence of the MgIn 2 S 4 /TiO 2 nanoarray
heterojunction improved visible light absorption, resulting in a ~ 6.8-fold increase
in photocurrent compared with a more conventional TiO 2 electrode. Ferrocene, an
electron donor employed as a label, has been used to accelerate electron–hole separation and thus enhance the photocurrent in PEC biosensors. In particular, Wei’s
group [15] reported the cytosensing of RAW264.7 macrophage cells utilizing a TiO 2
nanoneedles@MoO 3 array p–n heterojunction. MoO 3 is a p-type semiconductor
with a relatively wide band gap of 2.9 eV; its absorption peak is near to the UV light
region. Coupling MoO 3 with TiO 2 yielded a p–n heterojunction that promoted visible light absorption due to the offset of 2.61 eV between the valence band (VB) of
TiO 2 and the conduction band (CB) of MoO 3 . Immobilizing F4/80 antibodies used
4
Reprinted from the journal