Signal Off Research Articles

Fabrication of a novel electrochemical immunosensor for the sensitive detection of carcinoembryonic antigen using a double signal attenuation strategy

Carcinoembryonic antigen (CEA), an acidic protein, is a characteristic antigen produced by the tumor of various cancers (eg, breast, cervical, rectal, lung, etc.). Therefore, the detection of cancer antigens is very important for the early diagnosis and treatment of cancer. In this study, a novel of “signal off” strategy for electrochemical immunosensor was developed to detect CEA. To this end, Prussian blue nanoparticles (PB NPs), an electroactive substance, were used as the immunological platform. In addition, CuO2@SiO2 nanocomposites, which release Cu2+ and H2O2 under acidic conditions, were synthesized. The generated Cu2+ can replace the high spin iron (FeIII) in PB NPs, which in turn reduces the oxidation peak current of PB NPs. Due to the peroxidase-like nature of PB NPs, they can react with self-generated H2O2 to generate hydroxyl radicals (·OH), which can further convert 4-chloro-1 naphthol (4-CN) into a non-conductive polymer that accumulates on the electrode surface, this leads to a further reduction in the electrical signal of the PB NPs. Moreover, the self-generated Cu2+ and H2O2 can reduce the introduction of exogenous substances and improve the detection accuracy. Square wave voltammetry (SWV) revealed that the electrical signal of PB NPs gradually decreased with increasing CEA concentration. In addition, the electrical signal of PB NPs exhibited a good linearity in the range from 0.01 pg mL−1 to 80 ng mL−1, where in the logarithm of CEA concentration and the detection limit was as low as 0.0032 pg mL−1.

Signal “on-off-off” strategy for improving the sensitivity of BRCA1 electrochemical detection by combining gold substrate amplification, DNA conformational transformation and DSN enzymatic hydrolysis dual reduction

In this article we proposed a new signal amplification strategy based on signal “on-off-off” for improving the detection sensitivity of breast cancer 1 (BRCA1) electrochemical sensor. First, the stem-loop structured captured DNA (C-DNA) modified by 5′ sulfhydryl group and 3′ methylene blue (MB), was self-assembled on electrodeposited nanoAu surface through Au–S reaction. Electrodeposition of nanoAu increased electrode area and strengthened MB electrochemical signal, which indicated “signal on”. Then, BRCA1 hybridization with C-DNA made MB away from nanoAu surface, and reduced the MB signal due to the formation of stiff C-DNA/BRCA1 hybridized structure, which indicated “signal off”. Finally, the double strand specific nuclease (DSN) was used to cleave C-DNA/BRCA1, and led to the further decrease of MB signal, which also indicated “signal off”. Results showed that the designed sensor based on signal “on-off-off” had excellent detection sensitivity for BRCA1. The relative percentage change of MB reduction peak current was linear with BRCA1 concentration from 5 nM to 70 nM, and a low detection limit of 52 pM was achieved. The proposed sensor could distinguish single base mismatch BRCA1, two base mismatch BRCA1, and non-complementary DNA well. In addition, the sensor showed good reproducibility and stability.

A novel “signal off–triggered on” Förster resonance energy transfer biosensor for the ratiometric detection of pathogenic bacteria

Pathogenic bacterial infections pose a greatly threat to human health. Here, a novel “signal off–triggered on” Förster resonance energy transfer (FRET) ratiometric fluorescent sensor was developed for the selective detection of Staphylococcus aureus (S. aureus). Dual-recognition units, vancomycin hydrochloride (Van) anchor and aptamer affinity, enabled this sensor to accurately recognize S. aureus from other bacteria. The spectral overlap between the absorption of gold nanoclusters (Au NCs) and the emission spectrum of Ru(bpy)32+ enabled the occurrence of “signal off–triggered on” FRET, in which Au NCs were used as the energy donor and Ru(bpy)32+ as the energy acceptor, accompanied with the fluorescence quenching of Au NCs at 450 nm (“signal off” readout mode) and the signal increase of Ru(bpy)32+ at 610 nm (“signal on” readout mode). By measuring the F450 nm/F610 nm ratio, a wide linear range of 10 to 108 CFU/mL and a low detection limit of 1.0 CFU/mL were obtained for S. aureus. Satisfactory detection results in food samples and human serum, as well as ratiometric imaging of S. aureus, demonstrated the potential applications of the sensor in the early recognition of pathogenic microorganisms.

Electrochemical “signal on/off” paper-based aptasensor for ochratoxin A detection based on MXene-Au and Pt@NiCo-LDH-catalyzed signal amplification

Electrochemical sensing technology integrated with a paper-based analytical device (PAD) offers an effective method for analyte detection. Nevertheless, it is still challenging to realize reliable and sensitive analysis owing to the basic shortcomings (inferior conductivity and high batch-to-batch variability) of paper-based working electrodes (WE) and lack of efficient signal amplification label. Herein, we proposed a novel electrochemical aptasensor to detect ochratoxin A (OTA), with MXene-Au as sensing substrates and Pt nanoparticles (NPs) anchored hollow structure NiCo-layered double hydroxides (Pt@NiCo-LDH) as signal amplification materials. The complementary DNA (cDNA) was firstly assembled onto the MXene-Au/WE via Au-S bonds. Then aptamer (apta)-binding Pt@NiCo-LDH with excellent peroxidase (POD)-like activity was immobilized through hybridization to trigger the “signal on” state, generating a significant electrochemical signal. The presence of OTA enabled the dissociation of the apta-cDNA hybrid, releasing signal amplification labels to achieve “signal off” state. Based on the “signal on/off” strategy, the aptasensor exhibited a wider linear range from 20 fg/mL to 100 ng/mL and a lower limit of detection of 8.9 fg/mL (S/N = 3). This work provided a new avenue for the versatile design of electrochemical paper-based platform that enabled the on-site detection of various analytes.

A label free, signal off electrochemical aptasensor for amphetamine detection

Prescription stimulant drug (PSD) abuse is a worldwide concern, as they are clinically prescribed for psychological conditions and can be consumed recreationally without supervision. Easy accessibility of PSD procurement is also affecting the incidence of drug addiction among young and adult populations. Hence, there is a great need for the development of sensitive, rapid, and low-cost kits for on-spot PSD detection. In this study, a gold nanoflower modified, electrochemical aptasensor was constructed for Amphetamine (AMP) detection. The aptasensor was developed by covalent immobilization of thiolated AMP-specific aptamers (AMP-Apt) on AuNFs as a sensing interface. This configuration also enhanced aptamer density (6.37 ± 0.31 × 1012 molecules/cm2) on the electrode and low limit of detection of 0.51 nM in the linear range of 0.1-1.0 nM and sensitivity 0.501 nM/μA. The effect of potentially interfering compounds on the determination of AMP was found to be negligible for biological molecules and chemical entities. The aptasensor was successful in detecting AMP spiked urine and water samples with a recovery of 99-104% and 94.3-105% respectively. To our knowledge, this is the first label-free, gold nanoflowers modified electrochemical aptasensor for AMP detection and can be adapted for testing potential PSDs in the future.

DNA walker induced “signal off” electrochemical cytosensor strategy for ultrasensitive detection of tumor cells

The fragments of molecular motors can be transported and operated autonomously along a track. Most molecular walker systems are assembled from DNA building modules, exhibiting great potential applications in biocomputing, drug transport, sensing, etc. Hereby, we report a DNA walker driven by endonuclease Nt.BbvC I that can autonomously induce “signal off” sensing platform for highly sensitive detection of tumor cells. DNA density and trajectory conformation can affect DNA walker properties. Molybdenum selenide@gold nanoparticles (MoSe2@AuNPs) are modified on the electrode surface as a scaffold to accommodate more hairpin probe (H1) and provide a good interface for DNA walking. Magnetic beads are used to enrich target tumor cells, release single-stranded DNA (S1) and trigger DNA walker-based amplification strategy. Upon addition of tumor cells, more DNA-methylene blue (DNA-MB) is cracked from the electrode surface. Benefiting from efficient electrode modification, magnetic enrichment, DNA walker and enzyme-assisted amplification, an ultra-high sensitivity electrochemical cell analysis is realized, with a detection limit of 2 cells mL−1. More importantly, this DNA walker strategy is available for tumor cell analysis in clinical samples, suggesting the potential diagnostic applications.

Development of a graphene oxide nanosheet and double-stranded DNA structure based fluorescent "signal off" aptasensor for ochratoxin A detection in malt.

A "signal off" fluorescent aptasensor based on graphene oxide (GO) nanosheet and double-stranded DNA structure was fabricated for OTA detection. In the absence of OTA, the aptamer and its complementary DNA (cDNA) formed double-stranded conjugates that could coexist with GO, presenting fluorescence responses. Then, the presented OTA was captured by the aptamers, causing the release of cDNA-FAM probes. The free probes were adsorbed by GO, leading to an OTA concentration-dependent fluorescence quenching through fluorescence resonance energy transfer. Under optimum conditions, the fluorescent aptasensor exhibited outstanding sensitivity with a LOD of 11pg/mL and a wide dynamic range of 0.04-30ng/mL. The selectivity of the aptasensor was confirmed against other four mycotoxins, and the feasibility and reliability were verified by determining OTA in the spiked malt samples with satisfactory recovery of 95.50%-112.05%. This aptasensing platform could be adapted to measure other mycotoxins by replacing the aptamer sequences for food safety.

A “signal off” aptasensor based on AuNPs/Ni-MOF substrate-free catalyzed for detection Enrofloxacin

• A “signal off” electrochemical aptasensor strategy for the detection of ENR is constructed. • AuNPs/Ni-MOF for electrode sensing platform preparation are used for catalyst thionine and signal amplification. • AuTSs acts as a bridge between cDNA and thionine, speeding up electron transfer. • The protocol possesses accepted specificity and can be applied in real sample. In this project, we developed an electrochemical aptamer sensor based on the coordinated catalysis toward thionine (Thi) of nickel metal-organic framework (Ni-MOF) and gold nanoparticles (AuNPs) to sensitively detect the enrofloxacin (ENR), which belonged to a third-generation quinolone antibiotic for treat diseases caused by bacteria. In order to improve the analytical performance of the sensor, Ni-MOF and gold AuNPs, as the substrate material, could increase the load of the aptamer (Apt) and synergistically catalyze thionine (Thi). Therefore, ultrathin sheets of gold triangular nanosheets (AuTNSs) were prepared as signal labeling materials, which were loaded with a large amount of Thi and complementary deoxyribonucleic acid (cDNA). With the help with Ni-MOF and AuNPs catalysis toward Thi, under optimal conditions, the aptasensor exhibited a massive detection range of 1×10 −2 pg·mL −1 to 1×10 3 pg·mL −1 (S/N = 3) and a detection limit of 5.6×10 −3 pg·mL −1 for ENR. Meanwhile, the proposed sensor has a high sensitivity, satisfactory repeatability and long-time stability, and could be well applied to the detection of food samples.

A new ratiometric electrochemical aptasensor for the sensitive detection of carcinoembryonic antigen based on exonuclease I-assisted target recycling and hybridization chain reaction amplification strategy

In this work, a novel ratiometric electrochemical aptasensor was designed on the basis of dual-amplification mechanism by using exonuclease I (Exo I)-assisted target recycling and hybridization chain reaction (HCR). The thiol-modified capture DNA (Cp-DNA) was fixed on the surface of the gold electrode (AuE) modified with gold nanoparticles (AuNPs) through Au-S bonds. The ferrocene (Fc)-labeled DNA (Fc-DNA) hybridized with Cp-DNA to form Fc-DNA/Cp-DNA duplex. The presence of carcinoembryonic antigen (CEA) led to the dissociation of Fc-DNA from Fc-DNA/Cp-DNA duplex and initiated Exo Ⅰ-assisted target recycling to digest Fc-DNA, so numerous Fc left away from the electrode surface and resulting in the “signal off” of Fc. Moreover, Cp-DNA was exposed to bind trigger DNA and initiate HCR with the presence of H1 and H2 probes, resulting in the intercalating of numerous methylene blue (MB) molecules and the “signal-on” of MB. This dual signal strategy significantly amplified the decrease of Fc signal and the increase of MB signal, achieving a linear range of 1 pg mL−1 to 100 ng mL−1 with a detection limit of 0.479 pg mL−1 (S/N = 3). Besides, the developed aptasensor exhibited high specificity, good stability and reproducibility. More importantly, the aptasensor had been applied in detection of CEA in diluted human serum and displayed satisfactory anti-interference property. By changing the corresponding aptamer sequences, the designed strategy can be employed to detect other targets, which holds promising application in clinical diagnosis.

A Novel Ratiometric Electrochemical Biosensor Using Only One Signal Tag for Highly Reliable and Ultrasensitive Detection of miRNA-21.

Herein, a novel ratiometric electrochemical biosensor with methylene blue (MB) as the only one signal tag was proposed for highly reliable and ultrasensitive detection of microRNA-21 (miRNA-21) under the assistance of an intelligent target-induced dual signal amplification (T-DSA). First, a small amount of target miRNA-21 could produce abundant mimic targets DNA S1 and Zn2+ through target-induced recycle and acid dissolution, respectively. Then, S1 triggered rolling circle amplification (RCA) to generate functional DNA nanospheres (DSP) encoded by DNAzyme and substrate sequence for loading numerous signal tag MB with a remarkable electrochemical signal (signal on), and the Zn2+ cofactor mediated the nonviolent DNAzyme-catalyzed cleavage of DSP to sharply release MB with obviously reduced electrochemical responses (signal off). Impressively, our strategy could controllably load and release the only signal tag MB through the well-designed DSP to effectively avoid the false positive responses caused by the non-ideal upright state of DNA probes connected to electrodes in traditional distance-dependent signal adjustment ratiometric strategies with two different signal tags. Meanwhile, with the aid of innovative T-DSA recycle and RCA-produced functional DSP, the detection sensitivity of this sensing platform was significantly improved. As a result, the proposed biosensor successfully realized highly reliable and ultrasensitive detection of miRNA-21 with a detection limit down to 26.7 aM, which shows exceptional promise in biological analysis and medical diagnosis.

Covalent organic framework linked with amination luminol derivative as enhanced ECL luminophore for ultrasensitive analysis of cytochrome c.

Cytochrome c (cyt c) plays a critical role in mitochondrial respiratory chain, whose absence is detrimental to electron transport and reduce adenosine triphosphate. For ultrasensitive detection of cyt c, sheet-like covalent organic frameworks (COFs) were prepared by orderly accumulation of 1,3,5-benzenetricarboxaldehyde (BTA) and p-phenylenediamine (PDA), and further grafted with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) - an electrochemiluminescence (ECL) emitter. Specifically, the morphology and structure of the COFs-ABEI were mainly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). In parallel, the optical properties of the emitter were certified by UV-vis absorbance spectroscopy, Fourier infrared spectroscopy (FTIR), fluorescence (FL), and ECL measurements, showing 2.25-time enhanced ECL efficiency over pure ABEI, coupled by illustrating the interfacial electron transport mechanism. On the above foundation, a label-free "signal off" ECL biosensor was constructed by virtue of the specific immune recognition between the aptamer of the target cyt c with its capture DNA (cDNA) anchored on the biosensing platform, exhibiting a wider linear range of 1.00 fg mL-1-0.10 ng mL-1 (R2 = 0.998) and a lower limit of detection (LOD) down to 0.73 fg mL-1. This work offers some constructive guidelines for sensitive bioassays of disease-related biomarkers in the clinical field.

DNA Walker Induced “Signal Off” Electrochemical Cytosensor Strategy for Ultrasensitive Detection of Tumor Cells

DNA Walker Induced “Signal Off” Electrochemical Cytosensor Strategy for Ultrasensitive Detection of Tumor Cells

A Novel “Signal Off–Triggered On” Förster Resonance Energy Transfer Biosensor for the Ratiometric Detection of Pathogenic Bacteria

A Novel “Signal Off–Triggered On” Förster Resonance Energy Transfer Biosensor for the Ratiometric Detection of Pathogenic Bacteria

A simple "signal off-on" fluorescence nanoplatform for the label-free quantification of exosome-derived microRNA-21 in lung cancer plasma.

Asimple nanoplatform based on molybdenum disulfide (MoS2) nanosheets, a fluorescence quencher (signal off), and a hybridization chain reaction (HCR) signal amplification (signal on) used for the enzyme-free, label-free, and low-background signal quantification of microRNA-21 in plasma exosome is reported. According to the sequence of microRNA-21, carboxy-fluorescein (FAM)-labeled hybridization probe 1 (FAM-H1) and hybridization probes 2 (FAM-H2) were designed with excitation maxima at 488nm and emission maxima at 518nm. MoS2 nanosheets could adsorb FAM-H1 and FAM-H2 and quenched their fluorescence signals to reduce the background signal. However, HCR was triggered when microRNA-21 was present. Consequently, HCR products containing a large number of FAM fluorophores can emit a strong fluorescence at 518nm and could realize the detection of microRNA-21 as low as 6pmol/L and had a wide linear relation of 0.01-25nmol/L. This assay has the ability of single-base mismatch recognition and could identify microRNA-21 with high specificity. Most importantly, this approach was successfully applied to the detection of plasma exosomal microRNA-21 in patients with lung cancer, and it is proposed that other targets can also be detected by changing the FAM-H1 and FAM-H2 corresponding to the target sequence. Thus, a novel, hands-on strategy for liquid biopsy was proposed and has a potential application value in the early diagnosis of lung cancer.

MicroRNA-Triggered Deconstruction of Field-Free Spherical Nucleic Acid as an Electrochemiluminescence Biosensing Switch.

Herein, a new field-free and highly ordered spherical nucleic acid (SNA) nanostructure was self-assembled directly by ferrocene (Fc)-labeled DNA tweezers and DNA linkers based on the Watson-Crick base pairing rule, which was employed as an electrochemiluminescence (ECL) quenching switch with improved recognition efficiency due to the high local concentration of the ordered nanostructure. Moreover, with a collaborative strategy combined with the advantages of both self-accelerated approach and pore confinement-enhanced ECL effect, the mesoporous silica nanospheres (mSiO2 NSs) were prepared to be filled with rubrene (Rub) as ECL emitters and Pt nanoparticles (PtNPs) as coreaction accelerators (Rub-Pt@mSiO2 NSs), which demonstrated high ECL response in the aqueous media (dissolved O2 as coreactant). When the SNA nanostructure was immobilized on the Rub-Pt@mSiO2 NSs-modified electrode, it presented a "signal off" state owing to the quenching effect of the Fc molecules. As a proof of concept, the SNA-based ECL switch platform was applied in the detection of microRNA let-7b (let-7b). Impressively, in the presence of the target let-7b, a deconstruction of the SNA nanostructure was actuated, causing the Fc to leave the electrode surface and achieved an extremely high ECL recovery ("signal on" state). Hence, a sensitive determination for let-7b was realized with a low detection limit of 1.8 aM ranging from 10 aM to 1 nM by employing the Rub-Pt@mSiO2 NSs-based ECL platform combined with the target-triggered SNA deconstruction, which also offered an ingenious method for the further applications of biomarker analyses.

A dual-signaling electrochemical ratiometric strategy combining “signal-off” and “signal-on” approaches for detection of MicroRNAs

A dual-signaling electrochemical ratio metric strategy was developed for detection microRNA-18a based on the duplex-specific nuclease-assisted target recycling and electrochemical atom transfer radical polymerization signal amplification. In the presence of target microRNA, RNA/DNA duplexes are formed, which become the substrate of the duplex-specific nuclease-assisted target recycling. Hence only the DNA strand is cleaved by duplex-specific nuclease enzyme, resulting in the throw away of methylene blue (MB) from the electrode (signal off) accompanied by releasing of target microRNA, which can be recycled in the next hybridization. The remaining piece of capture DNAs on the electrode surface hybridize with the Azide labeled-signal DNAs. “Click reactions” were carried out between 3-Butynyl-2-bromoisobutyrate and Azide to initiate the electrochemical atom transfer radical polymerization reaction. This process could bring a great number of ferrocenylmethyl methacrylate (FMMA) on the surface of electrode (signal on). The IFMMA/IMB value was proportionate to the microRNA-18a concentration and measured by square wave voltammetry.The promising potential of the proposed biosensor in clinical analyses was exhibited by its remarkable features such as strong performance, high specificity, agreeable storage stability, and notable selectivity in real sample evaluation with no pretreatment or amplification. Finally, our biosensing method offers such an application to be used for the early clinical diagnosis of Pancreatic Cancer.

An “on-off” signal-switchable electrochemiluminescence biosensor for ultrasensitive detection of dual microRNAs based on DNAzyme-powered DNA walker

Herein, an “on-off” signal-switchable electrochemiluminescence (ECL) biosensor for dual miRNAs (miRNA-21 and miRNA-155) detection was constructed based on carbon dots (CDs)-labeled DNA walker, which can effectively avoid problems of the signal overlap or limited available labels that general exist in multiplex assays. In the presence of miRNA-21, the CDs-DNA walker were captured on the electrode via nucleic acid hybridization, producing a strong ECL signal corresponding to miRNA-21 (signal on). For miRNA-155, the biosensor was pre-incubated with CDs-DNA walker and assistant DNA (DNA-21). Target miRNA-155 could trigger metal ion-dependent DNAzyme cleavage. With the assistance of Mn2+, the substrate strands were cleaved and CDs detached from the electrode, resulting in a reduced ECL signal (signal off). The interference of miRNA-21 was eliminated because no more CDs-DNA walker was added. As a result, benefiting from the signal amplification offered by the CDs-DNA walker and the inherent properties of ECL technique, this biosensor achieved low detection limits of 33 fM for miRNA-21 and 33 aM for miRNA-155. This paper also demonstrates the biosensor’s bioanalytical application for multiplex detection of miRNA-21/155 in human serum samples and the total RNA extraction solution from the human cancer cell lines.

The enhanced photoelectrochemical platform constructed by N-doped ZnO nanopolyhedrons and porphyrin for ultrasensitive detection of brain natriuretic peptide

Nowadays, brain natriuretic peptide (BNP-32) is fundamental to early cardiovascular clinical diagnosis, whose accurate assay is of significance by photoelectrochemistry (PEC) for the low background and high precision. Herein, a novel enhanced PEC platform was built by successive deposition of N-doped ZnO nanopolyhedra (N–ZnO NP) and protoporphyrin IX (PPIX). Specifically, the N–ZnO NP with a narrow bandgap of 2.60 eV was synthesized by direct calcination of zeolitic imidazole framework-8 (ZIF-8), and performed as the substrate to enhance the photocurrents of PPIX (as photosensitizer) whose photoelectron transfer pathway and enhanced PEC mechanism were studied in detail. Under such foundation, a label-free PEC aptasensor was developed by deposition of DNA aptamer onto the PEC platform and then ultrasensitive assay of BNP-32 based on a “signal off” model. The biosensor showed a wide linear range (1 pg mL−1- 0.1 μg mL−1) with a limit of detection (LOD) as low as 0.14 pg mL−1. This doping technique of ZnO nanomaterials provides some valuable guidelines for synthesis of advanced PEC probes in bioanalysis.

Chemiluminescence “signal-on-off” dual signals ratio biosensor based on single-stranded DNA functions as guy wires to detect EcoR V

Signal output mode is the important part of biosensor. In general, “signal on” and “signal off” are two common output modes. The development of dual signals-based ratio analysis as a powerful diagnostic tool has attracted widespread attention in the biosensor field in recent years. Dual signals ratio sensors with “signal on” and “signal off” are more favored because of their low background signal and better sensitivity and selectivity. In this study, inspired by the idea that EcoR V can cut specific sites of DNA to produce two corresponding fragments, and by using the capturing probe as guy wires, a reliable and sensitive method for EcoR V assay is developed based on the ratio of dual chemiluminescence (CL) signals for the first time. In particular, in the existence of the objective EcoR V, the substrate DNA would be degraded into two double stranded oligonucleotides with blunt ends which include the sequence I and the sequence II, then they can separately compete with two different corresponding capture probes on magnetic beads (MBs). One of capture probe hybridized with the sequence I containing more guanine (G) bases that reacted with the phenylglyoxal (PG) to produce chemical reaction which triggered a positive CL signal output I + CL as “signal-on”; another capture probe is priority to hybridize the sequence II, which triggered the weaker reporter DNA linked with horseradish peroxidase (HRP) probe to fall off the MBs, thereby outputting a negative CL signal I−CL as “signal-off”. By comparing the linear relation and the correlation coefficient, the I−CL/I + CL ratio method has better linear relation (0.01–10 U/mL) and higher sensitivity (0.0045 U/mL). In addition, this developed strategy of high selectivity which can directly detect low concentration of target EcoR V in human serum, and thus this dual ratio biosensor might offer a promising detection approach for clinical diagnostics.

Humidity-sensitive CsPbBr3 perovskite based photoluminescent sensor for detecting Water content in herbal medicines

Excessive water in herbal medicines (HMs) can cause pests infestation, mildew, and decomposition of active ingredients during storage. The classical detection methods for water content are still unsatisfactory due to the requirement of sophisticated manipulation, long time consumption and usage of large amounts of toxic toluene. Herein, hot injection method was adopted to synthesize humidity-sensitive CsPbBr3 perovskite, which was used to develop a novel photoluminescent (PL) sensor on a paper substrate for rapid detection of water content in HMs with a turn-off mode. Due to the strong ionic nature of CsPbBr3 and the high aqueous solubility of CsBr, CsPbBr3 perovskite is very unstable upon the exposure of water. The signal off can be attributed to the phase change from luminescent CsPbBr3 to non-luminescent CsPb2Br5 according to the results of XRD pattern analysis of CsPbBr3 perovskite before and after water exposure. The PL intensity of CsPbBr3 is linearly related to the water content within the range of 1–17 %. For Seutellaria baicalensis and Astragalus flavone, the detection limits are 0.75 % and 0.67 %, respectively. The results of recovery tests for the two HMs are within the range of 96.7–102.5 %. This work realizes the application of CsPbBr3 perovskite in the field of pharmaceutical analysis, and shows the application potential for the control of water content in other types of samples sensitive to humidity.