Figure Legends
Figure
1. The Shennong-1 robot for sewage sampling, enrichment, concentration,
nucleic acid extraction, and reverse transcription.
Figure 2. Principle of the PEC biosensor for the detection of
cDNA using CRISPR/Cas12a system.
Figure 3. Morphological and compositional characterization of
the electrodes. Scanning electron microscopy images of (A) the base
electrode and (B) the assembled electrode. Elemental mappings of (C) the
assembled electrode, (D) Cd, (E) Te, (F) Zn, and (G) S.
Figure 4. X-ray
photoelectron spectroscopy survey spectra of the electrodes. (A)
X-ray photoelectron spectroscopy
survey spectra of (i) the base electrode and (ii) the assembled
electrode. High-resolution XPS spectra of the assembled electrode for
(B) Cd 3d, (C) Te 3d, (D) Zn 2p, and (E) S 2p.
Figure 5. Optimization
of crRNAs. Fluorescence analysis of crRNAs introduced with (A) a single
mismatch at different sites targeting the SARS-CoV-2 wild-type cDNA
template and (B) a dual mismatch at different sites targeting the BA.2
and BA. 5 cDNA templates
Figure 6. Electrochemical and PEC characterization, and
detection performance of the fabricated biosensor. (A) Stepwise
electrochemical impedance spectroscopy and (B) photocurrent response
analysis of the fabricated
photoelectrochemical biosensor (a: Au NPs/rGO; b: ssDNA/Au NPs/rGO; c:
MCH/ssDNA/Au NPs/rGO; d: MCH/dsDNA/Au NPs/rGO; e: CdTe/ZnS
QDs/MCH/dsDNA/Au NPs/rGO; and f: CdTe/ZnS QDs/MCH/dsDNA/Au NPs/rGO +
Cas12a–crRNA–target DNA complex in
[Fe(CN)6]3−/4−. (C)
Photoelectrochemical responses of the biosensor to various
concentrations of target DNA (a: 0; b: 1.0 aM; c: 10.0 aM; d: 100.0 aM;
e: 1.0 fM; f: 10.0 fM; g: 100.0 fM; h: 1.0 pM; i: 10.0 pM; j: 100.0 pM;
and k: 1.0 nM). (D) Relationship between the change in signal (ΔI) and
the logarithm of the concentration of target DNA. Error bars represent
the standard deviation of triplicate measurements. Cas12a:
CRISPR-associated protein 12a; crRNA: CRISPR RNA; dsDNA: double-stranded
DNA; MCH: 6-mercaptohexanol; NPs: nanoparticles; QDs: quantum dots; rGO:
reduced graphite oxide; ssDNA: single-stranded DNA.
Figure 7. Selectivity, stability, and reproducibility of the
biosensor. (A) Selectivity of the photoelectrochemical biosensor
incubated with various sequences:
Omicron BA.5, Omicron BA.2,
Wild-type, MERS, H1N1,
H3N2, Influenza B, and HRSV. (B)
Photocurrent stability of the biosensor under consecutive off−on−off
illumination for 10 cycles. (C) Responses of the photoelectrochemical
biosensor’s photocurrent after different storage periods. (D)
Reproducibility of the fabricated photoelectrochemical biosensor.
Columns with different superscript
letters show significant differences (p < 0.05).
Figure 8. Evaluation of the photoelectrochemical biosensing
platform by real sample analysis. Detection of
the L452R mutation in the spike
gene of Omicron BA.5 in
24 sewage samples via (A) RT-PCR
and (B) the proposed biosensor.
Figure 9. PEC reaction mechanism elucidated via density
functional theory. (A) Top view and front view of
the CdTe/ZnS QDs crystal
structure model. (B) Calculated
band structures of the CdTe/ZnS QDs. (C) The specific transfer mechanism
of charge carriers.