1 3
Topics in Current Chemistry (2020) 378:28
as recognition molecules onto this system allowed RAW264.7 cells to be measured
directly by steric hindrance.
Another common strategy for enhancing PEC biosensing is dye sensitization.
For example, Tang’s group [12] reported an ultrasensitive PEC immunoassay of
CEA based on porphyrin-sensitized TiO 2 nanoparticles (NPs) (Fig. 1c). Linking the water-soluble species 5,10,15,20-tetra(4-sulfophenyl)-21H,23H-porphyrin
(TSPP) through its sulfo groups to the TiO 2 led to an improvement in photoelectron
transfer. Compared with TiO 2 , TSPP has a narrower band gap (2.8 eV) and absorbs
more strongly in the visible region due to its delocalized π-electron system. Closely
matched energy levels of TiO 2 and TSPP result in fast electron transfer and slow
charge recombination. The resulting system was then used in combination with
glucose oxidase (GOx)-labeled Ab 2 to fabricate a stable and sensitive PEC biosensor for the detection of CEA. When glucose was present, the GOx oxidized it to
H 2 O 2 , which scavenged photogenerated holes in TiO 2 at low potential, amplifying
the photocurrent. Liu et al. [19] demonstrated that adding a chelating assembly of
polydopamine (PDA) to the surfaces of rutile TiO 2 mesocrystals enhanced the PEC
performance of an immunoassay for zearalenone. The benzoquinone groups of the
PDA received photoelectrons from the TiO 2 mesocrystals and enhanced the photocathodic current. Due to its special chemical structure, PDA absorbs long-wavelength light, improving charge-carrier separation. Similarly, polymerized l-DOPA
(PD) [25] was applied to improve the enzymatic performance of a PEC glucose
sensor by coupling the PD to a core–shell gold nanorod@TiO 2 heterostructure.
The PD not only enhanced the light absorption of the PEC system but it also provided a biocompatible matrix for surface functionalization and biointeractions. The
core–shell heterostructure was found to efficiently assist interfacial charge transfer.
The photoactive current density of PD/AuNR@TiO 2 /FTO was about 8.4 times that
of TiO 2 /FTO and 2.6 times that of AuNR@TiO 2 /FTO. Immobilizing GOx and HRP
(horseradish peroxidase) on the composite yielded a sensitive enzymatic PEC sensor for glucose with a low detection limit. Yan [26] reported a turn-on PEC strategy
based on localized surface plasmon resonance (LSPR) enhancement and dye sensitization for detecting the activity of protein kinase A (PKA) under visible light
irradiation. In the presence of PKA and ATP, the kemptide on the TiO 2 /ITO was
phosphorylated and then linked with DNA-conjugated gold nanoparticle (AuNP)
probes. [Ru(bpy) 3 ]
2+
was intercalated into the DNA grooves, where it could absorb
visible light and generate photoexcited electrons and thus photocurrent under visible
light irradiation. Meanwhile, the AuNPs were able to load a considerable amount of
[Ru(bpy) 3 ]
2+
-intercalated DNA, which enhanced the photocurrent transfer efficiency
through LSPR.
This phenomenon is the collective oscillation of electron clouds in highly conductive metal nanoparticles under suitable light irradiation. For nanoparticles of
noble metals such as Ag and Au [27], this oscillatory resonance occurs at visible
wavelengths. Thus, these nanoparticles can facilitate electron transfer and electron–hole pair seperation via the LSPR effect. In 2014, Da et al. [14] reported a PEC
biosensing strategy that utilized TiO 2 nanowires decorated with Au NPs and was
based on surface plasmon resonance (Fig. 2a). In this method, Au NPs were attached
directly to TiO 2 nanowires, which led to double the photocurrent density compared
5
Reprinted from the journal
Topics in Current Chemistry (2020) 378:28
as recognition molecules onto this system allowed RAW264.7 cells to be measured
directly by steric hindrance.
Another common strategy for enhancing PEC biosensing is dye sensitization.
For example, Tang’s group [12] reported an ultrasensitive PEC immunoassay of
CEA based on porphyrin-sensitized TiO 2 nanoparticles (NPs) (Fig. 1c). Linking the water-soluble species 5,10,15,20-tetra(4-sulfophenyl)-21H,23H-porphyrin
(TSPP) through its sulfo groups to the TiO 2 led to an improvement in photoelectron
transfer. Compared with TiO 2 , TSPP has a narrower band gap (2.8 eV) and absorbs
more strongly in the visible region due to its delocalized π-electron system. Closely
matched energy levels of TiO 2 and TSPP result in fast electron transfer and slow
charge recombination. The resulting system was then used in combination with
glucose oxidase (GOx)-labeled Ab 2 to fabricate a stable and sensitive PEC biosensor for the detection of CEA. When glucose was present, the GOx oxidized it to
H 2 O 2 , which scavenged photogenerated holes in TiO 2 at low potential, amplifying
the photocurrent. Liu et al. [19] demonstrated that adding a chelating assembly of
polydopamine (PDA) to the surfaces of rutile TiO 2 mesocrystals enhanced the PEC
performance of an immunoassay for zearalenone. The benzoquinone groups of the
PDA received photoelectrons from the TiO 2 mesocrystals and enhanced the photocathodic current. Due to its special chemical structure, PDA absorbs long-wavelength light, improving charge-carrier separation. Similarly, polymerized l-DOPA
(PD) [25] was applied to improve the enzymatic performance of a PEC glucose
sensor by coupling the PD to a core–shell gold nanorod@TiO 2 heterostructure.
The PD not only enhanced the light absorption of the PEC system but it also provided a biocompatible matrix for surface functionalization and biointeractions. The
core–shell heterostructure was found to efficiently assist interfacial charge transfer.
The photoactive current density of PD/AuNR@TiO 2 /FTO was about 8.4 times that
of TiO 2 /FTO and 2.6 times that of AuNR@TiO 2 /FTO. Immobilizing GOx and HRP
(horseradish peroxidase) on the composite yielded a sensitive enzymatic PEC sensor for glucose with a low detection limit. Yan [26] reported a turn-on PEC strategy
based on localized surface plasmon resonance (LSPR) enhancement and dye sensitization for detecting the activity of protein kinase A (PKA) under visible light
irradiation. In the presence of PKA and ATP, the kemptide on the TiO 2 /ITO was
phosphorylated and then linked with DNA-conjugated gold nanoparticle (AuNP)
probes. [Ru(bpy) 3 ]
2+
was intercalated into the DNA grooves, where it could absorb
visible light and generate photoexcited electrons and thus photocurrent under visible
light irradiation. Meanwhile, the AuNPs were able to load a considerable amount of
[Ru(bpy) 3 ]
2+
-intercalated DNA, which enhanced the photocurrent transfer efficiency
through LSPR.
This phenomenon is the collective oscillation of electron clouds in highly conductive metal nanoparticles under suitable light irradiation. For nanoparticles of
noble metals such as Ag and Au [27], this oscillatory resonance occurs at visible
wavelengths. Thus, these nanoparticles can facilitate electron transfer and electron–hole pair seperation via the LSPR effect. In 2014, Da et al. [14] reported a PEC
biosensing strategy that utilized TiO 2 nanowires decorated with Au NPs and was
based on surface plasmon resonance (Fig. 2a). In this method, Au NPs were attached
directly to TiO 2 nanowires, which led to double the photocurrent density compared
5
Reprinted from the journal