Organic photoelectrochemical transistors (OPECTs) have garnered considerable attention in next-generation bioanalysis, offering inherent signal amplification and facile integration with diverse recognition elements. However, their practical application remains hindered by issues such as irreversible physicochemical alterations, electrode fouling, and limited reusability in complex biological matrices. Herein, we propose an innovative interface-decoupled organic photoelectrochemical transistor (ID-OPECT) sensor featuring an external photon-gating module for highly responsive and reusable biodetection. This physical decoupling strategy allows the colorimetric reaction to occur independently of the photogate interface, which not only achieves effective photon filtering to modulate the photoelectric response but also preserves the photosensitive surface from interference and contamination, thereby enabling repeated use. By integrating an I2-starch colorimetric module coupled with a multi-enzyme cascade, the incident light transmission can be modulated in response to acetylcholinesterase (AChE) activity and its inhibition by chlorpyrifos (CPF). Under optimized conditions, the developed ID-OPECT platform enables sensitive detection of AChE and CPF, with limits of detection of 14.60 U L-1 and 16.94 ppb, respectively, by monitoring distinct channel current responses. This work presents a conceptually new paradigm for designing advanced optoelectronic sensors with enhanced stability and reusability.

Anionic cyanine is an organic fluorescent dye with excellent optical properties. Compared to cationic cyanine, anionic cyanine has been less studied and applied due to the lack of modification sites. However, when the cyclohexene ring in the anionic cyanine skeleton is replaced by a tetrahydropyridine ring, the modification site will be added, forming a novel cyanine dye AHC-N-R with NIR emission. Photophysical properties show that this anionic cyanine retains the excellent optical properties of conventional cyanine and is expected to adjust the fluorescence emission by changing the substituent groups. Acrylates were introduced in this dye to synthesize the cysteine fluorescent probe AHC-NBn-AE. The amino and sulfhydryl groups in cysteine condense with acrylate to form 1,4-thiazepane analogs and release fluorophores AHC-NBn-OH, restoring fluorescence at 650 nm. The fluorescence recovery of the probe was linearly related to the concentration of cysteine for 0.3–50.0 μmol/L. The detection limit was 0.1 μmol/L (S/N = 3, n = 9). There was almost no interference with DL-homocysteine, glutathione and several common amino acids to cysteine. The cysteine content of the L-cysteine capsule was successfully tested. The recovery rate was 94.4 %–101.5 %.

A novel "off-on" ratiometric fluorescent aptasensor was established for adenosine detection based on fluorescence resonance energy transfer (FRET) between CdS QDs, DNA QDs as donor and graphene oxide (GO) as acceptor. Aminoriched DNA QDs covalently bonded to the carboxyl group on the edge of the GO, and with the absorption of the TGA-modified CdS QDs with aptamer (CdS QDs-apt) onto the GO surface via the 7C-7C stacking interaction. The fluorescence of both CdS QDs and DNA QDs were efficiently quenched due to FRET (turn off). When adenosine was present, the specific binding of the aptamer to the target preferentially that released the CdS QDs-apt from GO. The process would inhibit the FRET which contribute to the fluorescence of CdS QDs-apt recovery again (turn on), while the fluorescence intensity of DNA QDs only slightly altered and acted as the reference signal. Thus, a novel "off-on" ratiometric fluorescent aptasensor for adenosine detection was constructed accordingly. There was a good linearity relationship between the ratio of the FL intensity (F595 nm/F464 nm) and the concentration of adenosine in the range of 20.00-180.0 nmol/L with a detection limit of 1.3 nmol/L (S/N = 3, n = 9). Importantly, the feasibility of the developed aptasensor for selective detection of adenosine in serum and urine samples with satisfactory results. The recoveries were observed to be 97.04-100.2 %.

Epinephrine (EP) is an essential catecholamine in the human body. Currently, most EP detection methods are not suitable for in vivo detection due to material limitations. An organic small molecule fluorescent probe based on a chemical cascade reaction for the detection of EP was designed. Anionic heptamethine cyanine dye was selected as a fluorescent dye because of its NIR fluorescence emission with excellent biocompatibility. The secondary amine of EP nucleophilically attacks the carbonate of the probe with its stronger nucleophilicity and further undergoes intramolecular nucleophilic cyclization to release the fluorophore. Other substances containing only primary amines or no beta-OH lack reaction competitiveness due to their weaker nucleophilicity or inability to undergo further cyclization. The fluorescence recovery of the probe was linearly related to the EP concentration of 2-75 mu mol/L. The detection limit was 0.4 mu mol/L. The recovery rate was 94.78-111.32%. Finally, we successfully achieved bioimaging of EP in living cells and EP analogue in nematodes.

The functionalization of metal-organic frameworks (MOFs) with organic small molecules by in situ postsynthetic modification has garnered considerable attention. However, the precise engineering of recognition sites using this method remains rarely explored in optically controlled bioelectronics. Herein, employing the Schiff base reaction to embed the small molecule (THBA) into a Zr-MOF, we fabricated a hydroxyl-rich MOF on the surface of titanium dioxide nanorod arrays (U6H@TiO2 NRs) to develop light-sensitive gate electrodes with tailored recognition capabilities. The U6H@TiO2 NR gate electrodes were integrated into organic photoelectrochemical transistor (OPECT) sensing systems to tailor a sensitive device for bilirubin (I-Bil) detection. In the presence of I-Bil, coordination effects, hydrogen bonding, and pi-pi interactions facilitated strong binding between U6H@TiO2 NRs and the target I-Bil. The electron-donating property of I-Bil influenced the gate voltage, enabling precise control of the channel status and modulation of the channel current. The OPECT device exhibited exceptional analytical performance toward I-Bil with wide linearity ranging from 1 x 10(-16) to 1 x 10(-9) M and a low limit detection of 0.022 fM. Leveraging the versatility of small molecules for boosting the functionalization of materials, this work demonstrates the great potential of the small molecule family for OPECT bioanalysis and holds promise for the advancement of OPECT sensors.

Based on DNA bio-dots-induced aggregation of gold nanoparticles (AuNPs), a methionine (Met) photoelectrochemical (PEC) sensor with CS–GSH–CuNCs/TiO2 NPs as the photoelectric conversion element and AuNPs as the specific recognition element was constructed. First, a TiO2 NPs/ITO electrode and CS–GSH–CuNCs were prepared, and then the CS–GSH–CuNCs/TiO2 NPs/ITO photosensitive electrode was obtained by self-assembly. Next, DNA bio-dots were modified to the upper surface of the electrode using a coupling reaction to assemble the DNA bio-dots/CS–GSH–CuNCs/TiO2 NPs electrode. Amino-rich DNA bio-dots were used to induce the aggregation of AuNPs on the electrode surface via Au–N interactions and prepare the AuNPs/DNA bio-dots/CS–GSH–CuNCs/TiO2 NPs electrode. Due to the fluorescence resonance energy transfer (FRET) between CS–GSH–CuNCs and AuNPs, the complexation chance of electron-hole (e−-h+) pair in CS–GSH–CuNCs increased, which, in turn, led to a decrease in photocurrent intensity. When Met was present, AuNPs aggregated on the electrode surface were shed and bound to Met since the Au–S interaction is stronger than the Au–N interaction, resulting in the recovery of the photocurrent signal. Under optimal conditions, the photocurrent intensity of the PEC sensor showed good linearity with the logarithm of Met concentration in the range of 25.0 nmol/L–10.0 μmol/L with the limit of detection (LOD) of 5.1 nmol/L (S/N = 3, n = 10).

The turn-on fluorescence signal mechanism for detection of GSH.

An ascorbic acid (AA) sensor was constructed based on the fluorescence resonance energy transfer (FRET) between CdS quantum dots (CdS QDs) and polydopamine (PDA) to detect trace AA sensitively. FRET occurred due to the broad absorption spectrum of PDA completely overlapped with the narrow emission spectrum of CdS QDs. The fluorescence of CdS QDs was quenched and in the “off” state. When AA was present, the conversion of DA to PDA was hindered and the FRET disappeared, resulting in the fluorescence of CdS QDs in an “on” state. Importantly, the degree of fluorescence recovery of CdS QDs displayed a desirable linear correlation with the concentration of AA in the range of 5.0–100.0 μmol/L, the linear equation is y=0.0119cAA+0.3113, and the detection limit is 1.16 μmol/L (S/N = 3, n = 9). There was almost no interference with common amino acid, glucose and biological sulfhydryl small molecules to AA. Trace amount of AA in vitamin C tablets were determined and satisfactory results were obtained; the recoveries were observed to be 98.01–100.7%.

An off-on fluorescence aptasensor was developed for trace thrombin detection based on fluorescence resonance energy transfer (FRET) between CdS QDs and gold nanoparticles (AuNPs). Using DNA pairwise hybridization of the aptamer to the complementary DNA (cDNA), the CdS QDs (energy donor) were tightly coupled to the AuNPs (energy acceptor), resulting in the occurrence of FRET and there was a dramatic fluorescence quenching of CdS QDs (turn off). When the thrombin was added to the fluorescence aptasensor, the specific binding of the aptamer to the target formed a G-quadruplex that caused the AuNPs receptor to detach and the DNA duplex to be disassembled. The process would inhibit the FRET which contribute to the recovery of fluorescence (turn on) and an "off-on" fluorescence aptasensor for thrombin detection was constructed accordingly. Under optimal conditions, the fluorescence recovery showed good linearity with the concentration of thrombin in the range of 1.35-54.0 nmol L-1, and the detection limit was 0.38 nmol L-1 (S/N = 3, n = 9). Importantly, the fluorescence aptasensor presented excellent specificity for thrombin, and was successfully applied to the quantitative determination of thrombin in real serum with satisfactory recoveries of 98.60-102.2%.

A photoelectrochemical (PEC) sensor combining chitosan-coated and glutathione-protected copper nanocluster (CS-GSH-CuNCs) with peroxidase-like activity and xanthine oxidase (XAO) was developed for rapid detection of xanthine. Firstly, CS-GSH-CuNCs was prepared by glutathione (GSH) reduction using chitosan (CS) as protective agent, and then was modified on titanium dioxide nanoparticles (TiO2 NPs)/ITO electrode which was prepared by sintering titanium dioxide (TiO2) on the ITO electrode surface by high temperature calcination. After excited by light at 350 nm, the photoinduced electrons from the lowest unoccupied molecular orbital (LUMO) of CS-GSH-CuNCs were transferred to the conduction band of TiO2, which resulted in spatial separation of electron-hole and enhancement of photocurrent signal. XAO oxidizes xanthine to produce hydrogen peroxide (H2O2). Part of the photoinduced electrons from CS-GSH-CuNCs transferred and catalyzed the reduction of H2O2, resulting in the reduction of the photocurrent. Under optimal conditions, the PEC sensor exhibits good sensitivity and reproducibility with the limit of detection (LOD) of 6.6 nmol . L-1 and a relative standard deviation of 3.5 % for 10 replicate detections of 1.00 mu mol . L-1 xanthine and the linear range of 0.04-90.0 mu mol . L-1 for xanthine. Furthermore, the PEC sensor presents nice selectivity owing to its enzyme-like activity and was successfully applied to human urine, indicating its great potential for real sample analysis.

A dual recognition system with a fluorescence quenching of quantum dots (QDs) and specific recognition of molecularly imprinted polymer (MIP) for the detection of chloramphenicol (CAP) was constructed. MIP@SiO2@QDs was prepared by reverse microemulsion method with 3-aminopropyltriethoxysilane (APTS), tetraethyl orthosilicate (TEOS) and QDs being used as the functional monomer, cross-linker and signal sources, respectively. MIP can specifically recognize CAP, and the fluorescence of QDs can be quenched by CAP due to the photo-induced electron transfer reaction between CAP and QDs. Thus, a method for the trace detection of CAP based on MIP@SiO2@QDs fluorescence quenching was established. The fluorescence quenching efficiency of MIP@SiO2@QDs displayed a desirable linear response to the concentration of CAP in the range of 1.00~4.00 × 102 μmol × L−1, and the limit of detection was 0.35 μmol × L−1 (3σ, n = 9). Importantly, MIP@SiO2@QDs presented good detection selectivity owing to specific recognition for CAP, and was successfully applied to quantify CAP in lake water with the recovery ranging 102.0~104.0%, suggesting this method has the promising potential for the on-site detection of CAP in environmental waters.

构建了一种以硫化镉量子点(CdS QDs)和二氧化钛纳米颗粒(TiO2 NPs)为光敏材料的四环素光电化学适体传感器.以烧结和自组装方式将TiO2 NPs,CdS QDs修饰于ITO电极表面,制得CdS QDs/TiO2 NPs/ITO光敏电极.由于CdS QDs具有比TiO2 NPs更高的导带能级,当CdS QDs吸收420 nm的可见光被激发时,产生的光生电子(e-)将转入TiO2 NPs的导带能级,而空穴(h+)位于CdS QDs的价带能级,实现了e--h+对的分离,提高了光电转换效率.利用偶联反应将TC适体修饰于CdS QDs/TiO2 NPs/ITO光敏电极表面,适体分子所产生的空间位阻效应将抑制光电转换效率,导致光电流信号降低;而TC可与其适体发生特异性结合被电极上的适体捕获,使TC适体从光敏电极表面脱落,光电流信号因此得以恢复.结果表明:该方法在浓度为0.01～15.00μmol·L-1时呈良好的线性关系;检出限为4.2 nmol·L-1(S/N=3);加标回收率为97.6％～104.7％;且对土霉素、金霉素、氯霉素、氨苄西林等与TC相似抗生素具有较好的抗干扰能力.表明TC PEC适体传感器在检测牛奶和兽药等实际样品中的TC有较好的前景.

Kanamycin (Kana) is widely used as a veterinary medicine and its abuse causes a serious threat to human health, raising the urgent demand for detection of residual Kana in animal-derived food with high specificity and sensitivity. Here, we developed a photoelectrochemical (PEC) biosensor for rapid quantification of Kana, with lead sulfide quantum dots/titanium dioxide nanoparticles (PbS QDs/TiO2 NPs) as a photosensitive composite, a Kana-specific DNA aptamer as a functional sensor, and ruthenium(III) hexaammine (Ru(NH3)63+) as a signal booster. To prepare the PEC aptasensor, TiO2 NPs, PbS QDs, and polyethyleneimine (PEI) were respectively used to modify the indium tin oxide electrode, and then the amine-terminated aptamer probe was connected to the PEI via glutaraldehyde. Finally, Ru(NH3)63+ was attached on the surface of the aptamer to increase the photocurrent intensity. When Kana binds competitively with Ru(NH3)63+ to the aptamer immobilized on the surface of the aptasensor, Ru(NH3)63+ will be released from the aptamer, resulting in a decrease of the photocurrent signal. This PEC aptasensor exhibits a good linear relationship between the photocurrent shift and the logarithm of Kana concentration within the range of 1.0-300.0 nmol L-1, and the detection limit is 0.161 nmol L-1. Importantly, the PEC aptasensor presented good detection selectivity owing to specific interaction with Kana and was successfully implemented to quantify Kana in honey and milk, suggesting that the PEC aptasensor has the potential of rapid detection of residual Kana in animal-derived foods.

A tetraphenylporphyrin (TPP) doped PFBT polymer quantum dots (TP-Pdots) were synthesized via the reprecipitation method for photoelectrochemical (PEC) aptasensor detection of tetracycline (TC). The TP-Pdots exhibit a superior cathode photocurrent signal. TP-Pdots increase the separation of photo-generated charges, and improve photocurrent conversion efficiency, resulting in enhanced photocurrent response. The aptamer was used as a recognition element and TP-Pdots as a photoactive material to prepare a PEC aptasensor for sensitivity detection of TC. The PEC aptasensor was constructed by immobilizing TP-Pdots on ITO electrode and combining it with aptamer by EDC coupling. After the TC reacts specifically with the aptamer, causing the aptamer to fall off from the TP-Pdots /ITO electrodes surface and the photocurrent intensity restored. This PEC aptamer sensor possesses a wide linear range from 1.0 nmol.l(-1) to 1.0 x 10(4) nmol.l(-1) with the detection limit of 0.26 nmol.l(-1). Meanwhile, the PEC aptasensor was successfully used for the detection of tetracycline in honey. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

A method for detecting cysteine based on fluorescenceresonance energy transfer ( FRET) between DNA quantum dots ( QDs ) and polydopamine ( PDA ) was developed. Since the fluorescence emitted by DNA QDs was absorbed by the PDA molecule, FRET occurred, resulting in fluorescence quenching of DNA QDs , and leaving the DNA QDs in a fluorescent " off " state. In the presence of cysteine , the spontaneous oxidative polymerization from dopamine ( DA ) to PDA was blocked , the fluorescence of DNA QDs was restored , and the fluorescence was " on " state. Based on this , a cysteine fluorescence sensor was developed. The sensor had good selectivity to cysteine, and there was no interference between common amino acids and small biothiol molecules. The linear equation was y = 0. 0181x -0. 0185 in linear range of 10. 0 - 100. 0 mu mol/L. The limit of detection ( LOD ) was 1. 7 mu mol/L ( S/N = 3 ) . The method was successfully applied to determination of cysteine in human urine samples , with recoveries of 98. 6% -105. 9%.

A sensitive mercury ion (Hg2+) sensor was designed by using CdS QDs/TiO2 composite material as the photoelectric conversion unit. After the coupling of two inorganic semiconductors (CdS QDs and TiO2) with different band gaps, the performance of electrode has been improved. After excited by the specific wavelength of light, the electron in CdS QDs would be motivated from the valence band to the conduction band. Then the Excited state electron would move to TiO2 due to that the valence band of TiO2 was lower than CdS QDs. The spatial separation of the e(-)-h(+) pairs in the different semiconductors could retards their recombination, and thereby the photoelectric conversion efficiency would be improved. We constructed a sensitive sensor for Hg2+ by two complementary short. stranded DNAs. One of the DNA single strands (ONS1) was rich in T bases, and Hg2+ could specifically bind to the T base to form a T-Hg2+-T structure, thus ONS1 could not be paired with complementary single stranded DNA (ONS2) labeled by gold nanoparticles (AuNPs), inhibiting the decrease of photocurrent and achieving sensitive detection of Hg2+. The Hg2+ sensor displayed a linear range from 1.0x10(-10) mol/L to 1.5x10(-7) mol/L and a detection limit of 6.0x10(-11) mol/L (S/N = 3).

Polymer dots (Pdots) represent newly developed semiconductor polymer nanoparticles and exhibit excellent characteristics as fluorescent probes. To improve the sensitivity and biocompatibility of Pdots ratiometric pH biosensors, we synthesized 3 types of water-soluble Pdots: Pdots-PF, Pdots-PP, and Pdots-PPF by different combinations of fluorescent dyes poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly[(9,9-dioctyl-fluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadazole)] (PFBT), and fluorescein isothiocyanate (FITC). We found that Pdots-PPF exhibits optimal performance on pH sensing. PFO and FITC in Pdots-PPF produce pH-insensitive (λ = 439 nm) and pH-sensitive (λ = 517 nm) fluorescence respectively upon a single excitation at 380 nm wavelength, which enables Pdots-PPF ratiometric pH sensing ability. Förster resonance energy transfer (FRET) together with the use of PFBT amplify the FITC signal, which enables Pdots-PPF robust sensitivity to pH. The emission intensity ratio (I517/I439) of Pdots-PPF changes linearly as a function of pH within the range of pH 3.0 to 8.0. Pdots-PPF also possesses desirable reversibility and stability in pH measurement. More importantly, Pdots-PPF was successfully used for cell imaging in Hela cells, exhibiting effective cellular uptake and low cytotoxicity. Our study suggests the promising potential of Pdots-PPF as an in vivo biomarker.

In this study, a high fluorescence sensitivity and selectivity, molecularly imprinted nanofluorescent polymer sensor (MIP@SiO2 @QDs) was prepared using a reverse microemulsion method. 2,4,6-Trichlorophenol (2,4,6-TCP) was detected using fluorescence quenching. Tetraethyl orthosilicate (TEOS), quantum dots (QDs) and 3-aminopropyltriethoxysilane (APTS) were used as cross-linker, signal sources and functional monomer respectively. The sensor (MIP@SiO2 @QDs) and the non-imprinted polymer sensor (NIP@SiO2 @QDs) were characterized using infra-red (IR) analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The selectivity of MIP@SiO2 @QDs was examined by comparing 2,4,6-TCP with other similar functional substances including 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP) and 4-chlorophenol (4-CP). Results showed that MIP@SiO2 @QDs had better selectivity for 2,4,6-TCP than the other compounds. Fluorescence quenching efficiency displayed a good linear response at the 2,4,6-TCP concentration range 5-1000 μmol/L. The limit of detection (LOD) was 0.9 μmol/L (3σ, n = 9). This method was equally applicable for testing actual samples with a recovery rate of 98.0-105.8%. The sensor had advantages of simple pretreatment, good sensitivity and selectivity, and wide linear range and could be applied for the rapid detection of 2,4,6-TCP in actual samples.

Firstly, titanium dioxide nanoparticles ( TiO2 NPs) was modified to the surface of indium tin oxide ( ITO) electrode by high-temperature calcination to prepare TiO2 NPs/ITO electrode. And then sulfide quantum dots( PbS QDs) were modified to the surface of TiO2 NPs/ITO electrode by successive ionic layer adsorption and reaction( SILAR) cycle to prepare the PbS QDs/Ti02 NPs/ITO electrode. And it was used to detect glutathione( GSH). In this sensor, when PbS QDs are excited by 470 nm visible light, it will produce electrons ( e) and holes (11+). Immediately after, h+ will be captured by GSH in solution, and then GSH is oxidized into GSSH. Therefore, the recombination of electrons and holes were avoided effectively. Thus the photoelectric efficiency has been significantly improved. This sensor had satisfactory sensitivity and selectivity for GSH. what' s more, the detection range is 0. 06-1 mmol/L, and the detection limit ( LOD) is 4. 6 x 10-3 mmol/L( S/N= 3)

In this work, on the basis of a Cu2+-doped two-dimensional material-based heterojunction photoelectrode, a novel anodic photoelectrochemical (PEC) sensing platform was constructed for highly sensitive detection of endogenous H2S. Briefly, with g-C3N4 and TiO2 as representative materials, the sensor was fabricated by modifying g-C3N4/TiO2 nanorod arrays (NAs) onto the surface of fluorine-doped tin oxide (FTO) and then doping Cu2+ as a CuxS (x = 1, 2) precursor. After the binding of S2- with surface-attached Cu2+, the signal was quenched owing to the in situ generation of CuxS which offers trapping sites to hinder generation of photocurrent signals. Since the photocurrent inhibition was intimately associated with the concentration of S2-, a highly sensitive PEC biosensor was fabricated for H2S detection. More importantly, the proposed sensing platform showed the enormous potential of g-C3N4/TiO2 NAs for further development of PEC bioanalysis, which may serve as a common basis for other semiconductor applications and stimulates the exploration of numerous high-performance nanocomposites.