Ratiometric Strategy Research Articles

Rational design of carbon dot nanozymes for ratiometric dual-signal and smartphone-assisted visual detection of nitrite in food matrices

Developing reliable nitrite (NO2−) sensors is essential for food safety and reducing health risks from NO2− exposure. In this study, we strategically designed nitrogen-doped carbon dot (N-CD) nanozymes to establish an accessible dual-signal ratiometric sensing system for detecting NO2− in food matrices. This system utilizes the photoluminescence and enzyme-like properties of N-CD nanozymes combined with NO2−-triggered diazotization reactions of substrates such as o-phenylenediamine (OPD) or 3,3′,5,5′-tetramethylbenzidine (TMB). The resulting N-CD/OPD and N-CD/TMB composites provide dual-mode detection—fluorescence and colorimetric—with high selectivity for NO2− and excellent resistance to interference. These sensors exhibit clear color changes under both ultraviolet and visible light, and can be combined with smartphones for visual, on-site detection of NO2−. By incorporating a ratiometric strategy, dual-signal output, and smartphone compatibility, our system achieved a low detection limit (≤ 1.92 μM) and satisfactory recovery rates (85.6–115 %) in environmental water and food samples. This highlights the potential of smartphone-assisted sensors for environmental monitoring and food safety applications. Our carbon dot-based platform offers a practical and effective solution for on-site NO2− detection, contributing valuable insights to the field.

Single-Band Ratiometric Thermometry Strategy Based on the Completely Reversed Thermal Excitation of O2- → Eu3+ CTB Edge and Eu3+ 4f → 4f Transition.

Single-band ratiometric (SBR) strategies present huge potential in the field of luminescence intensity ratio thermometry owing to their excellent signal discrepancy and appealing simplicity. Herein, we employ the approach of Na replacing Li in the LiYGeO4:Eu3+ phosphor to regulate the thermal stability of the O2- → Eu3+ charge-transfer band (CTB) and obtain significant thermal enhancement of luminescence under CTB edge excitation. Combined with the obvious thermal quenching of luminescence under ground-state absorption excitation, the ratio of the single emission band increases by 18 times when the temperature increases from 300 to 570 K. Therefore, such excitation-wavelength-dependent diametrically opposite thermal luminescence behaviors enabled SBR thermometry, whose maximum relative sensitivity can reach up to 3.6% K-1. We demonstrate that the O2- → Eu3+ CTB thermal red-shifts and enhancements are particularly attractive for SBR thermometry with high sensitivity by utilizing the diametrically reversed thermal excitation between the O2- → Eu3+ CTB edge and the 4f → 4f transition of Eu3+. These advances have opened up a novel horizon for the development of high relative sensitivity and performance of the SBR thermometry strategy.

Cupric ion coordination-mediated molecularly imprinted electrochemical sensor for the recognition and ratiometric detection of lidocaine

Molecularly imprinted polymers (MIPs) have been widely used as artificial recognition elements in sensing applications. However, their electrochemical sensing performance is generally hampered by limited affinity and uncontrolled condition change. In this work, a novel MIP electrochemical sensor based on metal coordination interaction was prepared and used for the recognition and ratiometric detection of lidocaine (LC). The sensor was constructed by electrodepositing Cu-coordinated MIP on biomass carbon modified glassy carbon electrode. Herein, Cu2+ ions acted as anchor for the immobilization of LC during the synthesis process, enabling the orderly formation of molecular recognition sites. Reversely, the metal coordination between Cu2+ ions and LC molecules facilitated the recognition of LC. Moreover, the doped cupric ions in the polymer film could provide a reference signal for subsequent ratiometric strategy. Thus the resulting sensor exhibited high selectivity, sensitivity, satisfactory reproducibility, and anti-interference ability. Under the selected conditions, the peak current ratio of LC and cupric ion was linear to LC concentration in the range of 0.008–2.5 μmol L−1 (R2 = 0.9951), and the limit of detection was 1.9 nmol L−1 (S/N = 3). The practical feasibility of the sensor was evaluated by detecting human serum and pharmaceutical samples, and satisfactory outcomes were obtained.

High-Precision Moisture Sensing in Tetrahydrofuran with Dual-Emissive Carbon Dots: Leveraging Ratiometric Strategy and Aggregation-Induced Emission

High-Precision Moisture Sensing in Tetrahydrofuran with Dual-Emissive Carbon Dots: Leveraging Ratiometric Strategy and Aggregation-Induced Emission

High-Frequency Quartz Crystal Microbalance and Dual-Signaling Electrochemical Ratiometric Assays of PTP1B Activity Based on COF@Au@Fc Hybrids.

The abnormal expression of protein tyrosine phosphatase 1B (PTP1B) is highly related to several serious human diseases. Therefore, an accurate PTP1B activity assay is beneficial to the diagnosis and treatment of these diseases. In this study, a dual-mode biosensing platform that enabled the sensitive and accurate assay of PTP1B activity was constructed based on the high-frequency (100 MHz) quartz crystal microbalance (QCM) and dual-signaling electrochemical (EC) ratiometric strategy. Covalent-organic framework@gold nanoparticles@ferrocene@single-strand DNA (COF@Au@Fc-S0) was introduced onto the QCM Au chip via the chelation between Zr4+ and phosphate groups (phosphate group of the phosphopeptide (P-peptide) on the QCM Au chip and the phosphate group of thiol-labeled single-stranded DNA (S0) on COF@Au@Fc-S0) and used as a signal reporter. When PTP1B was present, the dephosphorylation of the P-peptide led to the release of COF@Au@Fc-S0 from the QCM Au chip, resulting in an increase in the frequency of the QCM. Meanwhile, the released COF@Au@Fc-S0 hybridized with thiol/methylene blue (MB)-labeled hairpin DNA (S1-MB) on the Au NPs-modified indium-tin oxide (ITO) electrode. This caused MB to be far away from the electrode surface and Fc to be close to the electrode, leading to a decrease in the oxidation peak current of MB and an increase in the oxidation peak current of Fc. Thus, PTP1B-induced dephosphorylation of the P-peptide was monitored in real time by QCM, and PTP1B activity was detected sensitively and reliably using this innovative QCM-EC dual-mode sensing platform with an ultralow detection limit. This platform is anticipated to serve as a robust tool for the analysis of protein phosphatase activity and the discovery of drugs targeting protein phosphatase.

A dual-signaling surface-enhanced Raman spectroscopy ratiometric strategy for ultrasensitive Hg2+ detection based on Au@Ag/COF composites

Heavy metal ion pollution poses significant risks to human health and ecological systems, and its monitoring is important. A sensitive and accurate surface-enhanced Raman spectroscopy (SERS) detection assay for Hg2+ was developed using Au@Ag/COF substrates and Y-shaped DNA labeled with two Raman reporters. The Au@Ag NPs in the COF produced robust and uniform E-fields, improving their detection reproducibility. The Y-shaped DNA design increased sensitivity with a low detection limit of 5.0 × 10−16 M by bringing the Raman reporter closer to the substrate surface. Additionally, the use of two Raman reporters allowed for a ratiometric method, improving detection accuracy by detecting both “signal-off” and “signal-on” signals. This selective sensor exhibited excellent recovery in river water, tap water, and milk samples, showcasing its robust biosensing capability for the detection of Hg2+ and its potential for sensing other heavy-metal ions in food and environmental applications.

A novel strategy for ratiometric determination of o-phenylenediamine via in-situ fluorogenic reaction and generation of metal nanoparticles

Herein, a novel ratiometric strategy for ultra-sensitive detection of o-phenylenediamine (OPD) was proposed based on combinatorial reactions of in-situ fluorogenic reaction and in-situ formation of red fluorescent dithiothreitol-copper nanoparticles (DTT-CuNPs). Here, Cu2+ is used both as an oxidant and as a precursor. Dehydroascorbic acid (DHAA) is formed via redox reaction of AA and Cu2+. Then, DHAA reacts with OPD to yield blue fluorescent quinoxaline (OXD) with emission peak at 434 nm through in-situ fluorogenic reaction. Red emitting DTT-CuNPs with emission peak at 666 nm is instantly generated due to the coordination reaction between DTT and the residual Cu2+ which is not consumed by AA. The fluorescence intensity (FI) of OXD at 434 nm is closely relied on the concentration of OPD, which can be used as a response signal for OPD detection. Meanwhile, FI of DTT-CuNPs at 666 nm has no significant change, which can be used as a reference signal for OPD detection. Thus, the ratio (F434/F666) of the Cu2+/AA/DTT sensing system is successfully employed to quantify OPD, exhibiting a wide linear range from 0.2 µM to 60 µM, with LOD of 0.09 µM.

A Novel CRISPR/Cas12a-Mediated Ratiometric Dual-Signal Electrochemical Biosensor for Ultrasensitive and Reliable Detection of Circulating Tumor Deoxyribonucleic Acid.

Circulating tumor DNA (ctDNA) holds great promise as a noninvasive biomarker for cancer diagnosis, treatment, and prognosis. However, the accurate and specific quantification of low-abundance ctDNA in serum remains a significant challenge. This study introduced, for the first time, a novel exponential amplification reaction (EXPAR)-assisted CRISPR/Cas12a-mediated ratiometric dual-signal electrochemical biosensor for ultrasensitive and reliable detection of ctDNA. To implement the dual-signal strategy, a signal unit (ssDNA-MB@Fc/UiO-66-NH2) was prepared, consisting of methylene blue-modified ssDNA as the biogate to encapsulate ferrocene signal molecules within UiO-66-NH2 nanocarriers. The presence of target ctDNA KRAS triggered EXPAR amplification, generating numerous activators for Cas12a activation, resulting in the cleavage of ssDNA-P fully complementary to the ssDNA-MB biogate. Due to the inability to form a rigid structure dsDNA (ssDNA-MB/ssDNA-P), the separation of ssDNA-MB biogate from the UiO-66-NH2 surface was hindered by electrostatic interactions. Consequently, the supernatant collected after centrifugation exhibited either no or only a weak presence of Fc and MB signal molecules. Conversely, in the absence of the target ctDNA, the ssDNA-MB biogate was open, leading to the leakage of Fc signal molecules. This clever ratiometric strategy with Cas12a as the "connector", reflecting the concentration of ctDNA KRAS based on the ratio of the current intensities of the two electroactive signal molecules, enhanced detection sensitivity by at least 60-300 times compared to single-signal strategies. Moreover, this strategy demonstrated satisfactory performance in ctDNA detection in complex human serum, highlighting its potential for cancer diagnosis.

Molecularly imprinted ratiometric electrochemical sensor based on 3D-1D MoS2@CNTs hetero-nanoflower for selective detection of trimethoprim

Trimethoprim (TMP) is a broad-spectrum antibiotic that is frequently found residue in the environment and food. An innovative electrochemical sensor was proposed for the detection of trimethoprim with high selectivity, sensitivity and reproducibility through the integration of the flower-like MoS2@CNTs heterostructure as substrate, molecular imprinted polymer (MIP) technology as recognition, and the ratiometric strategy between trimethoprim and ferrocene (Fc) for quantitative. The recognition reaction of TMP by MIP-MoS2@CNTs sensor was assumed as an irreversible electrochemical oxidation reaction controlled by a combination of adsorption-diffusion process with two electrons and protons. With the incorporation of Fc during detection, a satisfying linear relationship of ITMP/IFc and the concentration of TMP was achieved, indicating a detection concentration ranging from 50 to 3000 nmol·L−1 with a detection limit of 27.01 nmol·L−1. In addition, the MoS2@CNTs MIP ratiometric sensor exhibited good stability for 20 days and excellent reproducibility with a relative standard deviation of 1.06 %, which was lower than 3.89 % of single signal. The practical feasibility of the sensor was detected in water samples with recovery rates of 98.62 ∼ 107.47 % and fish samples with recovery rates of 98.93 ∼ 105.45 %. Overall, the developed MIP ratiometric sensor provides a versatile system with easy operation and great potential for detecting small hazardous molecules in the environment and food products.

An enzyme-free and ratiometric biosensor for single nucleotide polymorphism with portable electrochemical system

Portable, low-cost and efficient biosensing systems are valuable for single nucleotide polymorphisms (SNPs) analysis, particularly in resource-limited fields. Herein, a rapid, enzyme-free and ratiometric SNPs biosensor with portable electrochemical system enabling simultaneous recognition and signal amplification is proposed. To demonstrate its versatility and effectiveness, we have selected the human cancer-related KRAS gene and the soybean mosaic virus resistance Rsv3 gene as our analysis models. Our biosensor is constructed based on a combination of strand displacement reactions and hybridization chain reactions (HCR). This unique design enables to differentiate between mutant (MT) and wild (WD) sequences based on the differential release of HCR products on the electrode surfaces. Importantly, this enzyme-free SNPs biosensor concurrently achieves both SNPs recognition and signal amplification, significantly reducing the reaction time to just 40 minutes. Furthermore, we have developed a miniaturized biosensor system that incorporates screen printed gold electrodes (SPGE) and smartphones. This system is integrated with a ratiometric strategy with an limit of detection as low as 1.2 fM, enhancing accuracy and eliminating external interference. This simple SNPs biosensing system possesses high reliability, positioning it as a versatile biosensor for the determination of various SNPs mutations.

Homogeneous electrochemical ratiometric biosensor for MircoRNA detection based on UiO-66-NH2 signal probe and waste-free entropy-driven DNA machine

The construction of efficient methods for highly sensitive and rapid detection of disease markers is essential for the early diagnosis of serious diseases. In this paper, taking advantage of the UiO-66-NH2 signal molecule in combination with a waste-free entropy-driven DNA machine, a novel homogeneous electrochemical ratiometric platform is developed to detect MircoRNA (miRNA). Metal-organic framework materials (UiO-66-NH2 MOF) and ferrocene were utilized as electrochemical signal tags and reference probes, respectively. The target-initiated waste-free three-dimensional (3D) entropy-driven DNA nanomachine is activated in the presence of miRNA, resulting in DNA-labeled-UiO-66-NH2 falling off from the electrode, leading to a decrease in the signal of UiO-66-NH2 at 0.83V. Our strategy can mitigate false positive responses induced by the DNA probes immobilized on electrodes in traditional distance-dependent signal adjustment ratiometric strategies. The proposed ratiometric platform demonstrates superior sensitivity (a detection limit of 9.8 fM), simplified operation, high selectivity, and high repeatability. The ratiometric biosensor is also applied to detect miRNA content in spiked serum samples.

A novel ratiometric electrochemical immunosensor for the detection of cancer antigen 125 based on three-dimensional carbon nanomaterial and MOFs

Accurate and sensitive detection of cancer antigen 125 (CA125) is important in early ovarian cancer diagnosis and monitoring. In the present work, a novel electrochemical ratiometric immunosensor for the determination of CA125 based on three-dimensional reduced graphene oxide/multi-walled carbon nanotube carboxylic acid- thionine (3DrGO/MWCNTs-Thi) and UIO-66-NH2/ferrocenecarboxylic acid (UiO-66-Fc) was constructed. 3DrGO/MWCNTs-Thi of immobilized primary antibody (Ab1) and UiO-66-Fc of labeled second antibody (Ab2) were used as capture probes and signaling probes for CA125, respectively. As the concentration of CA125 increases, the oxidation peak currents (IThi and IFc) generated by the two materials were changed in opposite directions, and therefore the ratio of the currents (IThi/IFc) was negatively correlated with the concentration of CA125. Thanks to the amplification of high loading of signaling molecules by the framework nanocomposites and the ratiometric strategy, the constructed electrochemical immunosensor exhibits outstanding accuracy, stability, and sensitivity. Under optimal conditions, the detection range spanned from 0.01 U mL−1 to 80 U mL−1, with a calculated limit of detection (LOD) of 0.0089 U mL−1. The immunosensor was successfully applied to real serum sample tests, indicating its potential for clinical detection applications.

Ratiometric electrochemical immunoassay based on 2D Co/Fe MOF decorated with toluidine blue and Fc-labeled Schiff base for accurate assay of alpha-fetoprotein in clinical serum

The high level of alpha-fetoprotein (AFP) expression is closely related to hepatocellular carcinoma (HCC). Herein, a dual signal ratiometric electrochemical immunosensor based on chitosan-ferrocenecarboxaldehyde-spindle gold (Chit-Fc-SAu) and Co/Fe metal-organic framework-toluidine blue/polydopamine (Co/Fe MOF-TB/PDA) was proposed for quantitative analysis of AFP. Specifically, Chit-Fc-SAu worked as a substrate to trap more primary antibodies (Ab1) generating the first electrochemical signal from Fc. Thanks to the large specific surface area, the synergistic and electronic effects of Co/Fe MOF nanosheets, and the rich functional groups of PDA, Co/Fe MOF-TB/PDA could load more secondary antibodies (Ab2) and signal molecules (TB) providing another amplified electrochemical signal. In the presence of AFP, Ab1-AFP-Ab2 formed a sandwich structure, and as the AFP concentration increased, the peak current ratio of TB to Fc (ITB/IFc) also increased. The dual signal ratiometric strategy can avoid environmental signal interference and achieve signal self-calibration, thereby improving the accuracy and reproducibility of detection. After a series of exploration, this self-calibrated ratiometric immunosensor exhibited a wide linear range (0.001−200 ng mL−1), a low detection limit (0.34 pg mL−1), and good repeatability. When applied to the assay of clinical serum samples, the detection results of ratiometric sensor were consistent with that of commercial electrochemiluminescence (ECL) immunoassay, significantly superior to that of non-ratiometric sensor. The self-calibrated strategy based on ratiometric sensor helps to improve the accuracy of AFP in clinical diagnosis.

Wavelength-Resolved Janus Biosensing Interface for Ratiometric Electrochemical Analysis.

The Janus interface, comprising multiple functional heterointerfaces with contrasting functionalities within a single interface, has recently garnered widespread research interest. Herein, a Janus biosensing interface is obtained via wavelength-resolved laser illumination. Deoxyribonucleic acid bridges the electrochemical probe of methylene blue (MB) and plasmonic gold nanoparticles (AuNPs), achieving a sensitive detection performance. MB shows differential electrochemical signals under front (I532front) and back (I650back) laser illumination at 532 and 650 nm, respectively, owing to the selective wavelength-resolved effect. Thus, the presence of a wavelength-resolved laser enabled the design of a biosensing interface with Janus properties. The change in the distance between MB and AuNPs induced by aflatoxin B1 (AFB1) indicates that a sensitive response of the Janus biosensing interface can be achieved. A ratiometric strategy is introduced to describe the electrochemical signals of the I532front and I650back for improved robustness. The obtained linear range is 0.0005-50 ng mL-1, with a detection limit of 0.175 pg mL-1. Our study demonstrated that the wavelength-resolved Janus interface enables an electrochemical biosensor with excellent sensitivity. This finding provides an efficient approach for improving biosensor performance.

Ratiometric strategy assisted electrochemical detection of 4-nitrophenol in water samples using nanostructured CuO

A ratiometric relationship between Cu redox centers (Cu1+ to Cu2+) and 4-NP reduction was systematically monitored on CuO/GCE. The selectivity and reliability of the sensing matrix in real sample conditions assure practical applications.

A label-free ratiometric fluorescent aptasensor based on a peroxidase-mimetic multifunctional ZrFe-MOF for the determination of tetrodotoxin.

A Fe/Zr bimetal-organic framework (ZrFe-MOF) is utilized to establish a ratiometric fluorescent aptasensor for the determination of tetrodotoxin (TTX). The multifunctional ZrFe-MOF possesses inherent fluorescence at 445nm wavelength, peroxidase-mimetic activity, and specific recognition and adsorption capabilities for aptamers, owing to its organic ligand, and Fe and Zr nodes. The peroxidation of o-phenylenediamine (OPD) substrate generates fluorescent 2,3-diaminophenazine (OPDox) at 555nm wavelength, thus quenching the inherent fluorescence of ZrFe-MOF because of the fluorescence resonance energy transfer (FRET) effect. TTX aptamers, which are absorbed on the material surface without immobilization or fluorescent labeling, inhibit the peroxidase-mimetic activity of ZrFe-MOF. It causes the decreased OPDox fluorescence at 555nm wavelength and the inverse restoration of ZrFe-MOF fluorescence at 445nm wavelength. With TTX, the aptamers specifically bind to TTX, triggering rigid complex release from ZrFe-MOF surface and reactivating its peroxidase-mimetic activity. Consequently, the two fluorescence signals exhibit opposite changes. Employing this ratiometric strategy, the determination of TTX is achieved with a detection limit of 0.027ng/mL and a linear range of 0.05-500ng/mL. This aptasensor also successfully determines TTX concentrations in puffer fish and clam samples, demonstrating its promising application for monitoring trace TTX in food safety.

Fluorine-doped carbon dots (F-CDs) adsorbing DNA via hydrophobic interaction play dual-role of quenching carrier and signal reference for ratiometric fluorescence strategy to detect microRNA

The expression levels of microRNAs (miRNA) can provide insights into the occurrence, progression, and treatment efficacy in tumors, highlighting the need for precise and easily controllable detection methodologies. The reasonable design of carbon dots enables the precise manipulation of luminescence and surface characteristics. Herein, fluorine doped carbon dots (F-CDs) were designed and prepared to establish a reasonable control of the interaction force between DNA and F-CDs. F-CDs were synthesized through a hydrothermal reaction involving tetrafluoroterephthalic acid and tetraethylene pentaamine, resulting in noteworthy optical and amphiphilic properties. F-CDs proficiently interact with single-stranded DNA (ssDNA) through hydrophobic interaction, leading to the quenching of dye labeled ssDNA, while maintaining self-fluorescence stability. The quenching mechanism was elucidated. The complementary DNA sequence induced nearly 100% desorption of ssDNA from F-CDs. Assisted by the target cycling signal amplification from duplex specific nuclease (DSN) and the self-fluorescence of F-CDs, an effective ratiometric strategy utilizing the adsorption system of F-CDs and probe DNA for let-7a was established for detecting let-7a, a critical miRNA in the assessment of tumor development. Under the optimized conditions, this method demonstrated high sensitivity and reproducibility in detecting let-7a with the linear range from 1.0 fM to 10.0 nM and a low limit of detection (LOD) of 3.0 fM. The recovery of let-7a in plasma and the evaluation of let-7a levels in seven cell types underscored the method's potential for efficient applications in monitoring of miRNA levels in real samples.

Ratiometric antifouling electrochemical biosensors based on designed Y-shaped peptide and MXene loaded with Au@ZIF-67 and methylene blue.

Based on the designed inverted Y-shaped peptide and MXene nanocomposite (MXene-Au@ZIF-67), a ratiometric anti-pollution electrochemical biosensor was designed and applied to the detection of biomarkers in serum. Au@ZIF-67 inserted into the interior of MXene can not only prevent the accumulation of MXene but also provide a large amounts of binding sites for capturing biomolecules. A designed multifunctional Y-shaped peptide containing anchoring, antifouling, and recognition sequences was anchored onto MXene-Au@ZIF-67 through Au-S bonds. Electrochemical signal molecules, ferrocenecarboxylic acid (Fc) and methylene blue (MB), were modified to another end of multifunctional peptide and interior of MXene-Au@ZIF-67, respectively, to produce aratiometric electrochemical signal. We selected prostate specific antigen (PSA) as the modelcompound. PSA specifically recognizes and cleaves the recognition segment in the Y-shaped peptide, and the signal of Fc is reduced, while the signal of MB remains unchanged. The ratiometric strategy endows the present biosensorhigh accuracy and sensitivity with adetection limit of 0.85pg/mL. In addition, the sensing surface has good antifouling ability due to the antifouling sequence of the two branching parts of the Y-shaped peptide. More importantly, by replacing the recognition segment of peptides alsoother targetsare accessible, indicating the potential application of the universal detection strategy tothe detection of various biomarkers in clinical diagnosis.

A novel ratiometric electrochemical aptasensor based on M-shaped functional DNA complexes for simultaneous detection of trace lead and mercury ions in series aquatic edible vegetables

Simultaneous quantification of multiple heavy metal ions (HMIs) is essential due to enhanced toxicity induced by synergistic effects. The currently available detection methods suffer from drawbacks such as costly devices, poor anti-interference, and specificity. In this work, a ratiometric electrochemical aptasensor for simultaneous detection of trace lead (Pb2+) and mercury ions (Hg2+) was developed. Here, a metal-organic framework, UiO-66-CNTs, with inherent and stable electrochemical signal was used for loading complementary strands (CSs) and internal reference. Guanine-rich and thymine-rich oligonucleotides, labelled with carbon dots (CDs), acted as aptamers (Apts) and hybridized with CSs to form M-shaped DNA complexes. Pb2+ and Hg2+ could be recognized and captured by Apts to form Pb2+-G-quadruplex and T-Hg2+-T complexes, leading to the destruction of M-shaped DNA complexes and changes in CDs’ signal. The current ratios, ICDs/IUiO-66-CNTs, were applied to quantify Pb2+ and Hg2+. Benefiting from the anti-interference ability of the ratiometric strategy and the specificity of Apts, the proposed method enabled detection Pb2+ and Hg2+ through simple instrumentation, with detection limits of 2.0 ng mL−1 and 0.5 ng mL−1. Moreover, it was applied to assess Pb2+ and Hg2+ contamination in series of aquatic edible vegetables. The experimental results were consistent with inductively coupled plasma-mass spectrometry (ICP-MS), demonstrating its potential in practical applications.

Self-Reporting Molecular Prodrug for In Situ Quantitative Sensing of Drug Release by Ratiometric Photoacoustic Imaging.

Understanding the pharmacokinetics of prodrugs in vivo necessitates quantitative, noninvasive, and real-time monitoring of drug release, despite its difficulty. Ratiometric photoacoustic (PA) imaging, a promising deep tissue imaging technology with a unique capacity for self-calibration, can aid in solving this problem. Here, for the first time, a methylamino-substituted Aza-BODIPY (BDP-N) and the chemotherapeutic drug camptothecin (CPT) are joined via a disulfide chain to produce the molecular theranostic prodrug (BSC) for real-time tumor mapping and quantitative visualization of intratumoral drug release using ratiometric PA imaging. Intact BSC has an extremely low toxicity, with a maximum absorption at ∼720 nm; however, endogenous glutathione (GSH), which is overexpressed in tumors, will cleave the disulfide bond and liberate CPT (with full toxicity) and BDP-N. This is accompanied by a significant redshift in absorption at ∼800 nm, resulting in the PA800/PA720 ratio. In vitro, a linear relationship is successfully established between PA800/PA720 values and CPT release rates, and subsequent experiments demonstrate that this relationship can also be applied to the quantitative detection of intratumoral CPT release in vivo. Notably, the novel ratiometric strategy eliminates nonresponsive interference and amplifies the multiples of the signal response to significantly improve the imaging contrast and detection precision. Therefore, this research offers a viable alternative for the design of molecular theranostic agents for the clinical diagnosis and treatment of tumors.