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The construction of robust photoelectrochemical (PEC) transducing platforms mediates the feasibility and performance of the PEC biosensors. In this work, perylene tetracarboxylic acid (PTA) nanoassemblies were exploited as robust semiconductors to form type II heterojunctions with In 2 O 3. The prepared organic/inorganic heterojunctions show high PEC transducing performances. The carboxyl groups of PTA avoid the additional surface functionalization for covalent immobilization of capturing elements which will diminish the transducing performance. This enables the facile construction of PEC immunosensing platforms. More importantly, Ag@CeO 2 nanoparticles were used as energy level matching nanolabels to develop a signal-on PEC immunosensing method. A linear response from 0.1 pg/mL to 100 ng/mL with a detection limit of 63.1 fg/mL was achieved for a typical protein biomarker carcinoembryonic antigen (CEA). • Sandwich-type immunoassay enables sensitive PEC detection. • PTA as robust semiconductors to form type II heterojunctions with In 2 O 3. • The carboxyl groups of PTA provide a large number of active sites. • The biosensor detection CEA exhibited the detection limit of 63.1 fg/mL. [ABSTRACT FROM AUTHOR]

• A sandwich-type signal off PEC sensor was constructed for PCT detection. • The photoactive matrix was Au NPs/BiOI NSs/B-TiO 2 NPs. • PbS/Co 3 O 4 was as a quenching signal label for signal amplification. • The PEC sensor exhibited a low detection limit of 0.02 pg/mL. A novel signal-off photoelectrochemical (PEC) immunosensor was proposed for procalcitonin (PCT) sensitive detection based on the Au nanoparticles/BiOI nanosheets/Black TiO 2 nanoparticles (Au NPs/BiOI NSs/B-TiO 2 NPs) as photoactive matrix and PbS quantum dots/Co 3 O 4 polyhedron (PbS/Co 3 O 4) as a quenching signal label for signal amplification. Concretely, BiOI NSs was fabricated by successive ionic layer absorption and reaction (SILAR) and formed the interlaced flake-like structure. Then Au NPs dropped on the BiOI NSs/B-TiO 2 NPs electrode forming Au NPs/BiOI NSs/B-TiO 2 NPs sensitization structure, which increased the utilization of visible light and accelerated electron transfer rate, resulting in a desirable PEC signal. PbS/Co 3 O 4 , an effective dual suppression signal quencher, was proposed for signal-off PEC immunosensor to weaken the photocurrent response because of the steric impedance, competitive absorption of light and competing consumption of electron donor. In this proposal, PCT was chosen to measure the performance of the suggested PEC immunosensor. Consequently, the fabricated PEC immunosensor showed a widely detection ranged from 0.1 pg/mL to 50 ng/mL and a low detection limit of 0.02 pg/mL (S/N = 3). What is more, the proposed PEC immunosensor possessed satisfactory selectivity, stability and reproducibility. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus (S. aureus) infections pose a serious threat to human health worldwide. Therefore, selective and accurate detection of S. aureus is necessary for preventing infections. Herein, we design the colorimetric-electrochemical sensing platform based on specific oligonucleotide (SA31 aptamer)-tunable oxidase-like activity of mesoporous polydopamine/MnO 2 (MPDA/MnO 2) nanozymes for the S. aureus detection. The MPDA/MnO 2 nanozymes possess excellent oxidase-like activity and electrochemical property. MPDA/MnO 2 nanozymes can catalyze the oxidation of TMB to generate TMB+ (blue color) and TMB2+ (yellow color) products. The oxidase-like activity of MPDA/MnO 2 can be inhibited when the SA31 is adsorbed on the surface of the nanozymes. In the presence of S. aureus, SA31 aptamer desorbs from MPDA/MnO 2 surface based on the specific identification between S. aureus and aptamer, resulting in the recovery of their oxidase-like activity. Based on the different oxidative degree of TMB, the color of sensing solution changes from blue to yellow, the electrochemical signals also have changed simultaneously. The colorimetric-electrochemical sensing platform can accurately detect S. aureus, showing a low detection limit in 3 CFU/mL (S/N = 3). Furthermore, the dual-mode sensing platform can be utilized for the accurate and specific detection of S. aureus in real sample with the recovery of 95.15%− 115.28%. This work based on SA31 aptamer-tunable oxidase-like activity of MPDA/MnO 2 nanozymes provides a dual-mode assay for specific and accurate detection of S. aureus. • A dual-modal strategy was designed to detect S. aureus based on the colorimetric-electrochemical sensing platform. • The SA31 can regulate the oxidase-like activity by adsorption and desorption on the surface of MPDA/MnO 2 nanozymes. • The electrochemical behavior of the electrode can be adjusted by the specific binding between aptamers and S. aureus. • This dual-modal sensing platform possesses low detection limit (3 CFU/mL) and wide linear range. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ultrasensitive electrochemical aptasensor was developed for detecting Pb2+. • Au@p-rGO was applied as support for immobilizing the aptamer. • Au NPs@GO as signal probe exhibited high electrocatalytic activity towards H 2 O 2. • The aptasensor displayed low detection limit of 1.67 pmol/L for Pb2+. Abstract A sensitive electrochemical aptasensor was designed based on gold modified graphene nanocomposite with different morphologies for the detection of lead ion (Pb2+). Specifically, a sulfydryl-labeled substrate strand (Apt1) and a sulfydryl-labeled catalytic strand (Apt2) were devised in fabricating the electrochemical aptasensor. Gold modified porous reduced graphene oxide (Au@p-rGO) was synthesized and applied as support for immobilizing the Apt1. And gold modified graphene oxide (Au NPs@GO) was employed as signal probe and connected with Apt2 to realize the immobilization of it on the electrode by means of the principle of complementary base pairing. The current signal can be obtained by recording the electrocatalytic conditions toward H 2 O 2. The Pb2+-dependent DNAzyme could play a role when Pb2+ existed. With the increase of the concentration of Pb2+, the current response revealed a diminishing signal, thus realizing the sensitive detection of Pb2+. Under the optimal conditions, the fabricated electrochemical aptasensor exhibited a linear response toward Pb2+ ranging from 5 pmol/L to 1 μmol/L, together with a low limit of detection of 1.67 pmol/L. Moreover, the prepared aptasensor displayed outstanding selectivity, acceptable stability and superior reproducibility for detecting Pb2+. This proposed tactics may provide reference and potential applications for detecting some other heavy metal ions. [ABSTRACT FROM AUTHOR]

An electrochemical biosensor was fabricated for reliable and highly sensitive microRNA-21 assay by catalytic hairpin assembly and Pd nanoparticles-DNA layered nanoreticulation, providing a new way in the biochemical assay for detecting microRNA-21 in early disease diagnosis. • The sensitive biosensor was constructed for the detection of miR-21 based on CHA and Pd NPs-DNA LNR. • This biosensor shows low limit of detection and wide dynamic correlation of miR-21, providing a powerful platform for detecting miR-21. • The proposed method was enzyme-free, PCR-free, and convenient without the requirement of any additional separation steps. Herein, a Pd nanoparticles-DNA layered nanoreticulation (Pd NPs-DNA LNR) sensor was assembled to a graphene oxide (GO)-modified electrode by catalytic hairpin assembly (CHA) and a self-assembly process. In this process, GO was modified on the electrode surface to provide -COOH sites for DNA bonding. Moreover, with the CHA circular amplification strategy, many single DNA1 were exposed to be able to be bound with Pd-DNA2 for the formation of the Pd NPs-DNA LNR, which enabled the ultrasensitive detection of microRNA-21 (miR-21) with a low limit of detection 63.1 aM. This strategy combines the amplification technology of CHA and Pd NPs-DNA LNR with Pd NPs. Such a layered nanoreticulation material can support abundant Pd NPs to avoid aggregation and obtain enhanced electrochemical signals. Significantly, this method can be successfully applied in tumor cell lysates and provides a neoteric channel for early disease diagnosis. [ABSTRACT FROM AUTHOR]

• This split-type sensor separates the two processes of antigen-antibody specific recognition and photoelectric conversion. • THCH as extra electron donor is released through the controlled-release strategy. • CdS sensitized Bi 2 Sn 2 O 7 forms a heterojunction as the matrix to provide basic PEC response effectively. • The biosensor for sensitive detection PCT exhibited the detection limit of 0.17 pg/mL. A split-type photoelectrochemical (PEC) sensor for procalcitonin (PCT) detection was successfully prepared. This split-type sensor adopted controlled-release strategy, which separated the two processes of antigen-antibody specific recognition and photoelectric conversion, so that the two processes can be performed independently. In addition, CdS sensitized Bi 2 Sn 2 O 7 is combined for the first time to form a heterojunction as the matrix to provide the basic PEC response, which could effectively absorb visible-light, and reduced electron-hole pair recombination, ensured the stability of the sensor. Distinctly important, the skillfully process was performed in a 96-well plate where the specific reaction was completed proceeded between antigen and antibody. For improving sensitivity of the sensor, acetylcholinesterase (ACHE) connected to SiO 2 nanospheres (SiO 2 NSs) modified by second antibody (Ab 2 -ACHE@SiO 2 NSs) was designed, the thiocholine (THCH) can be released when acetylthiocholine iodide (ATCH) exists, and the THCH as an electron donor could enhance PEC response. The proposed PEC immunoassay with high-performance photosensitive materials, and the smart electron donor released strategy have a wide detection liner range from 0.0005 to 100 ng/mL with a low detection limit of 0.17 pg/mL, also provide great clinical diagnostic potential for other target proteins. [ABSTRACT FROM AUTHOR]

• The signal indicator and matrix, Fe 3 S 4 -Pd, displayed excellent electrocatalytic activity for H 2 O 2 redox reaction. • Magnetic glassy carbon electrode was used to firmly immobilized the magnetic Fe 3 S 4 -Pd to achieve satisfied stability. • PBG nanomaterial played a role as the electron blocking label that realized a sensitive variation of current signal. • The signal-off sensing platform was successfully constructed, with a low detection limit of 130 fg/mL. Herein, a sandwich-type electrochemical (EC) immunosensor is proposed based on a special signal-off mode for the sensitive detection of procalcitonin (PCT) by utilizing Fe 3 S 4 loaded with Pd nanoparticles (Fe 3 S 4 -Pd) as a signal indicator and matrix and functionalized pineal mesoporous bioactive glass (PBG) as the label for signal amplification. Fe 3 S 4 -Pd not only shows excellent electrocatalytic activity for the H 2 O 2 redox reaction but is also firmly immobilized on a magnetic glassy carbon electrode due to its excellent magnetic properties; because of the above features, this immunosensor exhibits excellent sensitivity and stability, respectively. Glutaraldehyde is used as a cross-linking agent to bond the secondary antibodies (Ab 2) with PBG. It is worth mentioning that the electron transfer rate between the electrolyte and electrode is decreased significantly by PBG-Ab 2 ; thus, a sensitive variation in the current signal is observed, and a further improvement in the sensitivity of the immunosensor is realized. More importantly, the proposed signal-off sensing system has a wide linear detection range of 500 fg/mL to 50 ng/mL for PCT and a low detection limit of 130 fg/mL, which promotes it as a promising detection method for the sensitive detection of other biomarkers. [ABSTRACT FROM AUTHOR]

• Ultrasensitive electrochemical aptasensor was fabricated for detecting Pb2+. • AuPd@Fe-MOFs labeled DNA was firstly applied to produce the electrical signal. • Au@MoS 2 /rGO was utilized as sensing platform to construct the aptasensor. • The aptasensor displayed low detection limit of 0.07 pmol/L for Pb2+ detection. In this work, an electrochemical aptasensor was proposed by using gold-modified molybdenum disulfide/reduced graphene oxide (Au@MoS 2 /rGO) nanocomposite and gold-palladium (AuPd)-modified MIL-88 (Fe) metal-organic frameworks (AuPd@Fe-MOFs) for sensitive detection of lead ions (Pb2+). The 8–17 DNAzyme consisting of a substrate strand (Apt1) and a catalytic strand (Apt2) was used to construct the aptasensor. Au@MoS 2 /rGO nanocomposite was applied as the sensing platform to immobilize the mercapto-group-labeled Apt1. Meanwhile, AuPd@Fe-MOFs was employed to label Apt2, which showed excellent catalytic ability toward H 2 O 2. In the presence of Pb2+, the Apt1 of the DNAzyme was catalytically cut off, decreasing the amount of AuPd@Fe-MOFs. The current response was correlated to the Pb2+concentration, thereby achieving Pb2+ detection. Under the optimal experimental conditions, the fabricated aptasensor showed a highly linear response for Pb2+ in the range from 5.0 pmol/L to 2.0 μmol/L, with a detection limit of 0.07 pmol/L. Additionally, the proposed electrochemical aptasensor exhibited excellent selectivity, stability and reproducibility. Moreover, the proposed aptasensor demonstrated good performance in real water sample analysis, making it promising for use in Pb2+ detection in environmental monitoring. [ABSTRACT FROM AUTHOR]

• A PEC aptamer sensor for 17β-estradiol detection was introduced. • The Mo doped porous BiVO 4 nanoarray/Bi 2 S 3 as sensing platform for immobilization of aptamer. • The Mo-p BiVO 4 /Bi 2 S 3 presented a high PEC signal by supplying additional free electrons. • The nanoarray structure provided large specific surface area and large number of binding sites. • The PEC aptamer sensor exhibited a low detection limit of 3.2 × 10−4 pM. A new porous nanoarray is constructed as sensing platform of photoelectrochemical (PEC) biosensor for detection of 17β-estradiol (E2) by using aptamer. The molybdenum (Mo) ions doped into porous bismuth vanadate (Mo-p BiVO 4) nanoarray by electrodeposition of BiOI nanoarray. Then, the bismuth sulfide (Bi 2 S 3) nanoparticles are grown in-situ on the surface of Mo-p BiVO 4 by the self-sacrificial synthesis method to form novel Mo-p BiVO 4 /Bi 2 S 3 heterojunction. Herein, the Mo-p BiVO 4 /Bi 2 S 3 heterojunction presents a high PEC signal because of Mo-p BiVO 4 could increase electron-hole separation yield by supplying additional free electrons, furthermore the heterojunction of Mo-p BiVO 4 /Bi 2 S 3 could promote ultrafast transfer of charge and inhibit the recombination of e−/h+ pairs by presenting cascade band-edge levels under irradiation of the visible light. Moreover, the nanoarray structure has large specific surface area, which could accelerate electron transfer and provide large number of binding sites to immobilize aptamer. This PEC aptamer sensor exhibits high sensitivity with a detection limit 3.2 × 10-4 pM and a good photocurrent response toward target E2 in the range of 1 × 10-3 - 5 × 102 pM. Good specificity and stability are acquired for analysis of E2 in human urine. Importantly, this designed sensor platform of Mo-p BiVO 4 /Bi 2 S 3 heterojunction provides a new promising application for other environmental estrogen analysis. [ABSTRACT FROM AUTHOR]