Versatile T1-Based Chemical Analysis Platform Using Fe3+/Fe2+ Interconversion

Ni-Pt nanozyme-mediated relaxation and colorimetric sensor for dual-modality detection of norovirus

An NiPt nanozyme-mediated relaxation and colorimetric sensor is developed for dual-modality detection of norovirus (NoV). The relaxation modality is based on the "catalase-like" activity of the NiPt nanozyme, which adjusts the hydrogen peroxide (H2O2) mediated Fe (II)/Fe(III) conversion, thereby changing the relaxation signal. Poly-γ-glutamic acid (MW ≈ 1w) can enhance the relaxivity of Fe(III) (r1 = 7.11 mM-1 s-1; r2 = 8.94 mM-1 s-1). The colorimetric modality exploits the "peroxidase-like" activity of the NiPt nanozyme, which can catalyze the oxidation of colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) to blue oxTMB in H2O2. Under optimal conditions, the relaxation modality exhibits a wide working range (1.0 × 101-1.0 × 104 fM) and a limit of detection (LOD) of 4.7 fM (equivalent to 2820 copies/μL). The spiked recoveries range from 99.593 to 106.442 %, and the relative standard deviation (RSD) is less than 5.124 %. The colorimetric modality exhibited the same working range with a lower LOD of 2.9 fM (equivalent to 1740 copies/μL) and an RSD of less than 2.611 %. Additionally, the recombinase polymerase amplification reaction enabled the detection of low NoV levels in food samples with a working range of 102-106 copies/mL and LOD of 102 copies/mL. The accuracy of the sensor in the analysis of spiked samples is consistent with the gold standard method (real-time quantitative reverse transcription-polymerase chain reaction), demonstrating the high accuracy and practical utility of the sensor.

Nanoplasmonic biosensors for multicolor visual analysis of acetylcholinesterase activity and drug inhibitor screening in point-of-care testing

The monitoring of acetylcholinesterase (AChE) activity and the screening of its inhibitors are significance of the diagnosis and drug therapy of nervous diseases. A metal ions-mediated signal amplification strategy was developed for the highly sensitive and multicolor assay of AChE activity and visually screening its drug inhibitors. After the specific reaction between AChE and acetylthiocholine (ATCh), the hydrolysis product thiocholine (TCh) can directly and decompose the α-FeOOH nanorods (NRs) to release amounts of Fe2+, which was regarded as Fenton reagent to efficiently catalyze H2O2 to produce ·OH. Then, the as-formed ·OH can further largely shorten the gold nanobipyramids (Au NBPs), generating a series of palpable color variations. The linear range for AChE activity was 0.01-500.0 U/L with the limit of detection as low as 0.0074 U/L. The vivid visual effects could be easily distinguished for the multicolor assay of AChE activity by naked eye in visible light. To achieve the point-of-care testing, Au NBPs were further assembled on polymeric electrospun nanofibrous films (ENFs) surface as test strips for the easy-to-use test of AChE activity by RGB values with a smartphone. Fascinatingly, this proposed strategy can be used for the visual screening AChE inhibitors or non-inhibitors. Comparing with the clinical drugs (rivastigmine tartrate, and donepezil), some natural alkaloids such as evodiamine, caffeine, camptothecin, and berberine hydrochloride were selected as inhibitor modes to confirm the drug screening capability of this method. This proposed strategy may have great potential in the other disease-related enzymatic biomarkers assay and the rapid screening of drug therapy.

Magnetically Controlled and Addressable Photoelectrochemical Sensor Array with Self-Calibration for the Label-Free Detection of Amyloid β-Proteins

A label-free addressable photoelectric immunosensor array was designed for the detection of amyloid β-proteins based on magnetic separation and self-calibration strategies. In this paper, Na2Ti6O13 with a flower-like morphology was prepared by the hydrothermal method; after continuously combining Fe3O4 and CdS, it was endowed with magnetism and better photoelectric activity. Subsequently, a series of reactions occurred in the solution, and the magnetic separation method was used to enrich the target. On the other hand, the ITO glass was separated into eight sites (2 × 4) using magnets, and a light shield was utilized to prevent light exposure, resulting in addressable and continuous detection. After the uniform preparation of magnetic photoelectric materials and precise control of testing conditions, the relative errors among different sites have been effectively reduced. Moreover, incorporating a self-calibration strategy has allowed the sensor array to achieve greater accuracy. The proposed photoelectrochemical biosensor exhibits a good relationship with amyloid β-protein ranging from 0.01 to 100 ng mL-1 with a limit of detection of 1.1 pg mL-1 and exhibits excellent specificity, reproducibility, and stability.

A facile and sensitive magnetic relaxation sensing strategy based on the conversion of Fe3+ ions to Prussian blue precipitates for the detection of alkaline phosphatase and ascorbic acid oxidase

Herein, a novel magnetic relaxation sensing strategy based on the change in Fe³⁺ content has been proposed by utilizing the conversion of Fe³⁺ ions to Prussian blue (PB) precipitates. Compared with the common detection approach based on the valence state change of Fe³⁺ ions, our strategy can cause a larger change in the relaxation time of water protons and higher detection sensitivity since PB precipitate can induce a larger change in the Fe³⁺ ion concentration and has a weaker effect on the relaxation process of water protons relative to Fe²⁺ ions. Then, we employ alkaline phosphatase (ALP) as a model target to verify the feasibility and detection performance of the as-proposed strategy. Actually, ascorbic acid (AA) generated from the ALP-catalyzed L-ascorbyl-2-phosphate hydrolysis reaction can reduce potassium ferricyanide into potassium ferrocyanide, and potassium ferrocyanide reacts with Fe³⁺ to form PB precipitates, leading to a higher relaxation time. Under optimum conditions, the method for ALP detection has a wide linear range from 5 to 230 mU/mL, and the detection limit is 0.28 mU/mL, sufficiently demonstrating the feasibility and satisfactory analysis performance of this strategy, which opens up a new path for the construction of magnetic relaxation sensors. Furthermore, this strategy has also been successfully applied to ascorbic acid oxidase detection, suggesting its expansibility in magnetic relaxation detection.

Rapid estimation approach for glycosylated serum protein of human serum based on the combination of deep learning and TD-NMR technology

Rapid and precise estimation of glycosylated serum protein (GSP) of human serum is of great importance for the treatment and diagnosis of diabetes mellitus. In this study, we propose a novel method for estimation of GSP level based on the combination of deep learning and time domain nuclear magnetic resonance (TD-NMR) transverse relaxation signal of human serum. Specifically, a principal component analysis (PCA)-enhanced one-dimensional convolutional neural network (1D-CNN) is proposed to analyze the TD-NMR transverse relaxation signal of human serum. The proposed algorithm is proved by accurate estimation of GSP level for the collected serum samples. Furthermore, the proposed algorithm is compared with 1D-CNN without PCA, long short-term memory network (LSTM) and some conventional machine learning algorithms. The results indicate that PCA-enhanced 1D-CNN (PC-1D-CNN) has the minimum error. This study proves that proposed method is feasible and superior to estimate GSP level of human serum using TD-NMR transverse relaxation signals.

Nanoparticles derived from naturally occurring metal chelators for theranostic applications

Metals are indispensable for the activities of all living things, from single-celled organisms to higher organisms, including humans. Beyond their intrinsic quality as metal ions, metals help creatures to maintain requisite biological processes by forming coordination complexes with endogenous ligands that are broadly distributed in nature. These types of naturally occurring chelating reactions are found through the kingdoms of life, including bacteria, plants and animals. Mimicking these naturally occurring coordination complexes with intrinsic biocompatibility may offer an opportunity to develop nanomedicine toward clinical applications. Herein, we introduce representative examples of naturally occurring coordination complexes in a selection of model organisms and highlight such bio-inspired metal-chelating nanomaterials for theranostic applications.

Simultaneous Homogeneous Fluorescence Detection of AFP and GPC3 in Hepatocellular Carcinoma Clinical Samples Assisted by Enzyme-Free Catalytic Hairpin Assembly

Simultaneous sensitive and cost-effective detection of multiple tumor markers has shown great potential for cancer diagnostics. Herein, we reported a simple enzyme-free parallel catalytic hairpin assembly (CHA) amplification strategy with N-methyl mesoporphyrin IX (NMM) and quantum dots (QDs) as signal reporters for the homogeneous fluorescent simultaneous detection of alpha-fetoprotein (AFP) and glypican-3 (GPC3). Upon selective binding, the released single-stranded DNA (ssDNA) from the two-aptamer double-stranded DNA (dsDNA) probes triggers CHA amplification, further releasing the G-quadruplex sequence and Ag⁺ from the C-Ag⁺-C structures at the same time. Then, NMM and CdTe QDs selectively recognize G-quadruplex and Ag⁺, respectively. Under optimized conditions, limits of detections (LODs) as low as 3 fg/mL for AFP and 0.25 fg/mL for GPC3 were achieved using fluorescence readout. Using color- and distance-based visual readouts, an LOD of 1 fg/mL for GPC3 was reached. This method was applied to quantitatively analyze AFP and GPC3 in 41 clinical serum samples of hepatocellular carcinoma (HCC) patients. The quantitative test results for AFP and GPC3 were consistent with those obtained using the electrochemiluminescence immunoassay (ECL-IA) clinical kit and correlated with radiological and pathological findings. The results of clinical tests demonstrated the potential of GPC3 as a tumor biomarker, and we propose a cut-off value of 2 ng/mL GPC3 for HCC.

Fe(III)-Shikonin Supramolecular Nanomedicine for Combined Therapy of Tumor via Ferroptosis and Necroptosis

Most of the antitumor chemotherapeutic drugs execute the therapeutic performance upon eliciting tumor cell apoptosis, which may cause chemoresistance of tumors. Design of novel drugs to eradicate apoptosis-resistant tumors via non-apoptotic cell death pathways is promising for improving the long-term chemotherapeutic efficacy. Herein, a Fe(III)-Shikonin metal-polyphenol-coordinated supramolecular nanomedicine for combined therapy of tumor via ferroptosis and necroptosis is designed. The construction of the nanomedicine based on the coordinated self-assembly between Fe³⁺ and Shikonin not only overcomes the shortcomings of Shikonin including its low bioavailability and high toxicity toward normal tissues, but also integrates the theranostics functions of Fe ions. Under the exposure of the high concentration of glutathione (GSH) in tumor cells, the as-prepared nanomedicine will disassemble into Fe²⁺ and Shikonin, followed by stimulating the tumor cell death through ferroptosis and necroptosis. In addition, benefiting from the stealth effect of polyethylene glycol (PEG) and the targeting ability of cyclo(Arg-Gly-Asp-d-Phe-Lys) (cRGD) to α_v β₃ -integrin, NH₂ -PEG-cRGD-modified nanomedicine exhibits a GSH-responsive therapy toward 4T1 tumor in vivo and self-enhanced longitudinal relaxation (T₁ )-weighted imaging property. Since the self-assembly of natural Shikonin and human body-necessary Fe element is facile and feasible, the work may provide a promising supramolecular nanomedicine for next-generation chemotherapeutic applications.

Micromixer with Fine-Tuned Mathematical Spiral Structures

Micromixers with the microchannel structure can enable rapid and efficient mixing of multiple types of fluids on a microfluidic chip. Herein, we report the mixing performance of three passive micromixers based on the different mathematical spiral structures. We study the fluid flow characteristics of Archimedes spiral, Fermat spiral, and hyperbolic spiral structures with various channel widths and Reynolds number (Re) ranging from 0 to 10 via numerical simulation and visualization experiments. In addition, we analyze the mechanism of streamlines and Dean vortices at different cross sections during fluid flows. As the fluid flows in the Fermat spiral channel, the centrifugal force induces the Dean vortex to form a chaotic advection, enhancing the fluid mixing performance. By integrating the Fermat spiral channel into a microfluidic chip, we successfully detect acute myocardial infarction (AMI) marker with the double-antibody sandwich method and reduce the detection time to 10 min. This method has a low reagent consumption and a high reaction efficiency and demonstrates great potential in point-of-care testing (POCT).

Highly sensitive magnetic relaxation sensing method for aflatoxin B1 detection based on Au NP-assisted triple self-assembly cascade signal amplification

Highly sensitive detection of aflatoxin B₁ (AFB₁) is of great significance because of its high toxicity and carcinogenesis. We propose a magnetic relaxation sensing method based on gold nanoparticles (Au NPs)-assisted triple self-assembly cascade signal amplification for highly sensitive detection of AFB₁. Both AFB₁ antibody and initiator DNA (iDNA) are labeled on Au NPs to form Ab-Au-iDNA probe. iDNA is enriched by Au NPs to achieve first signal amplification. Different amounts of Ab-Au-iDNA were bound with AFB₁ antigen by indirect competitive immunoassay, and then hybridization chain reaction event was initiated by iDNA to produce long hybridization chain reaction products to enrich more horseradish peroxidase-streptavidin for the second signal amplification. Dopamine could be rapidly converted to polydopamine by HRP catalysis, which is used as the third signal amplification. The Fe³⁺ solution, providing paramagnetic ions with a strong magnetic signal, could be adsorbed by the polydopamine due to the formation of coordination bonds of phenolic hydroxyl groups with Fe³⁺. This effective interaction between polydopamine and Fe³⁺ significantly changes the transverse relaxation time signal of Fe³⁺ supernatant solution, which can be used as a magnetic probe for highly sensitive detection of AFB₁. The sensor exhibited high specificity and sensitivity with a detection limit of 0.453 pg/mL owing to the Au NP-assisted triple self-assembly cascade signal amplification strategy. It has been successfully employed for AFB₁ detection in animal feed samples with consistent results of enzyme linked immune sorbent assay and high-performance liquid chromatography.

Sensitive Oxidation of Sorbitol-Mediated Fe2+ by H2O2: A Reliable TD-NMR Method for Clinical Blood Glucose Detection

The clinical challenge of high-accuracy blood glucose detection schemes is to overcome the detection error caused by the background interferences in different individuals. H₂O₂ as the specific product of glucose oxidation can be involved in the Fe²⁺/Fe³⁺ conversion and detected by the time-domain nuclear magnetic resonance (TD-NMR) method sensitively. But, in clinical applications, the oxidation of Fe²⁺ is susceptible to the complex sample substrates. In this work, we sorted out two kinds of possible interference mechanisms of Fe²⁺ oxidation in the NMR blood glucose detection method and proposed a feasible scheme that uses sorbitol to weaken the adverse effects of interference. We found that sorbitol-mediated Fe²⁺ can greatly enhance the sensitivity of the T₂ value to H₂O₂. The chain reaction caused by sorbitol can significantly amplify the efficiency of Fe²⁺ oxidation at the same concentration of H₂O₂. Thereby, we can achieve the higher dilution multiple of serum samples to reduce the amount of interfering substances involved in the Fe²⁺/Fe³⁺ conversion. We justified the accuracy and availability of our method by successfully detecting and confirming the correlation between the T₂ decrease and glucose concentration of the serum samples collected from 16 subjects. The sorbitol-Fe²⁺ glucose detection method with high sensitivity can be further combined with miniature NMR analyzers to satisfy the calibration requirements of glucose monitoring in diabetic patients instead of frequent medical visits.

Point-of-Care Testing for Multiple Cardiac Markers Based on a Snail-Shaped Microfluidic Chip

Existing methods for detecting cardiac markers are difficult to be applied in point-of-care testing (POCT) due to complex operation, long time consumption, and low sensitivity. Here, we report a snail-shaped microfluidic chip (SMC) for the multiplex detection of cTnI, CK-MB, and Myo with high sensitivity and a short detection time. The SMC consists of a sandwich structure: a channel layer with a mixer and reaction zone, a reaction layer coated with capture antibodies, and a base layer. The opening or closing of the microchannels is realized by controlling the downward movement of the press-type mechanical valve. The chemiluminescence method was used as a signal readout, and the experimental conditions were optimized. SMC could detect cTnI, CK-MB, and Myo at concentrations as low as 1.02, 1.37, and 4.15. The SMC will be a promising platform for a simultaneous determination of multianalytes and shows a potential application in POCT.

A Microfluidic Chip-Based MRS Immunosensor for Biomarker Detection via Enzyme-Mediated Nanoparticle Assembly

Conventional immunoassay methods have their common defects, such as tedious processing steps and inadequate sensitivity, in detecting whole blood. To overcome the above problems, we report a microfluidic chip-based magnetic relaxation switching (MRS) immunosensor via enzyme-mediated nanoparticles to simplify operation and amplify the signal in detecting whole blood samples. In the silver mirror reaction with catalase (CAT) as the catalyst, H2O2 can effectively control the production of Ag NPs. The amount of Ag NPs formed further affects the degree of aggregation of magnetic nanoparticles (MNPS), which gives rise to the changes of transverse relaxation time (T2). Both sample addition and reagent reaction are carried out in the microfluidic chip, thereby saving time and reagent consumption. We also successfully apply the sensor to detect alpha-fetoprotein (AFP) in real samples with a satisfied limit of detection (LOD = 0.56 ng/ml), which is superior to the conventional ELISA.

Direct Transverse Relaxation Time Biosensing Strategy for Detecting Foodborne Pathogens through Enzyme-Mediated Sol-Gel Transition of Hydrogels

In this work, we develop a direct transverse relaxation time (T₂) biosensing strategy and employ it for assaying foodborne pathogens relying on the alkaline phosphatase (ALP)-mediated sol-gel transition of hydrogels. ALP can catalyze the reaction to generate an acidic environment to transform the sol-state alginate solution to hydrogel, and this hydrogelation process can directly regulate the diffusion rate of water protons that results in a T₂ change of water molecules. By means of enzyme-modulated sol-gel transition and antigen-antibody interactions, this T₂ biosensor displays high sensitivity for detecting 50 CFU/mL S. enteritidis within 2 h. This biosensing strategy directly modulates the water molecules rather than magnetic probes in traditional methods, offering a straightforward, novel, and sensitive platform for pathogen detection.

Double-enzymes-mediated Fe2+/Fe3+ conversion as magnetic relaxation switch for pesticide residues sensing

It is a great challenge to develop a newly rapid and accurate detection method for pesticide residues. In this work, based on acetylcholinesterase (AChE) and choline oxidase (CHO), a double-enzymes-mediated Fe²⁺/Fe³⁺ conversion as magnetic relaxation switch was explored for the measurement of acetamiprid residue. In the double-enzymes reactions, acetylcholine chloride (ACh) can be catalyzed to produce choline by AChE, which is successively hydrolyzed to betaine and hydrogen peroxide (H₂O₂) by CHO. According to the enzyme inhibition principle, AChE activity will be inactivated in the presence of acetamiprid, thus leading to the less production of H₂O₂. Wherein, Fe²⁺, ACh, AChE and CHO were optimized as the reaction substrates. In the reaction system, acetamiprid can be reflected by the transverse relaxation time (T₂) that related with H₂O₂ mediated Fe²⁺ variations, which was further developed as an enzyme cascade amplification method. The detection linear range is 0.01∼1000 μg mL^-1 (R² = 0.99), and the limit of detection (LOD) is 2.66 ng mL^-1 (S/N = 3, n = 3), behaving a 335-fold improvement in LOD than that of traditional enzyme inhibition method (0.89 μg mL^-1). This method can realize "one-step mixing" detection of acetamiprid, which makes it a promising analytical tool for monitoring pesticide residue in complicated samples.

Oxyhemoglobin nano-recruiter preparation and its application in biomimetic red blood cells to relieve tumor hypoxia and enhance photodynamic therapy activity

Photodynamic therapy (PDT) is strongly O2 dependent. Therefore, its therapeutic effects are seriously hindered in hypoxic tumors. Red blood cells are responsible for delivering O2 in the blood. In this manuscript, biomimetic red blood cells (BRBCs) were exploited using a layer-by-layer assembly method, using Fe3O4@CuO, oxyhemoglobin (OxyHb), a photosensitizer and a photo-cross linked acrylate modified hyaluronic acid (HA) gel shell. The Fe3O4@CuO core has very high OxyHb loading efficiency (the adsorption capacity of Fe3O4@CuO for OxyHb is derived to be 0.99 mg mg-1) to ensure a sufficient O2 supply. OxyHb was protected well by the HA shell in order to avoid O2 release during the delivery process in blood before arrival at the tumor tissue. The HA shell protection can be eliminated in position at the tumor to trigger O2 release through hyaluronidase (HAase) triggered HA degradation. Furthermore, Fe3O4 in the nanosystem can provide magnetic field assisted tumor targeting and magnetic resonance imaging of the tumor. Therefore, this work presents a highly efficient all-in-one biomimetic nanomedicine approach to overcome hypoxia and achieve tumor targeting theranostics.

Enzyme activity-modulated etching of gold nanobipyramids@MnO2 nanoparticles for ALP assay using surface-enhanced Raman spectroscopy

The detection of enzyme activity can provide valuable insights into clinical diagnosis. Herein, we synthesize gold nanobipyramids@MnO2 nanoparticles (AMNS) as the surface-enhanced Raman spectroscopy (SERS) substrate for the first time and design a "turn-on" SERS strategy for the detection of enzyme activity without the need for a complicated SERS nanotag preparation process. In the presence of alkaline phosphatase (ALP), 2-phosphate-l-ascorbic acid trisodium salt (AAP) can be hydrolyzed to ascorbic acid (AA), which can etch the shell of AMNS by reducing MnO2 to Mn2+. The cracked MnO2 shell-caused electromagnetic field enhancement from AMNS can give rise to a significant increase in the Raman intensity of the adsorbed molecules (i.e., crystal violet, CV) on the surfaces of nanobipyramids. Thus, the ALP activity can be accurately quantified based on the MnO2 shell thickness dependent Raman signal output from CV. A linear dynamic range from 0.4 to 20 mU mL-1 with a detection limit of 0.04 mU mL-1 is achieved, which is more sensitive than other spectroscopic methods for ALP detection. Because of its advantages of sensitivity, convenience and versatility, this approach provides a new perspective to disease-related biomolecular detection in the future.

Background Signal-Free Magnetic Bioassay for Food-Borne Pathogen and Residue of Veterinary Drug via Mn(VII)/Mn(II) Interconversion

Paramagnetic ion-mediated sensors can greatly simplify current magnetic sensors for biochemical assays, but it remains challenging because of the limited sensitivity. Herein, we report a magnetic immunosensor relying on Mn(VII)/Mn(II) interconversion and the corresponding change in the low-field nuclear magnetic resonance (LF-NMR) of the transverse relaxation rate (R₂). The fact that the NMR R₂ of the water protons detected in Mn(II) aqueous solution is much stronger than Mn(VII) aqueous solution enables the modulation of the LF-NMR signal intensity of R₂. By employing immunomagnetic separation and enzyme-catalyzed reaction, this Mn(VII)/Mn(II) interconversion allows the development of a background signal-free magnetic immunosensor with a high signal-to-background ratio that enables detection of ractopamine and Salmonella with high sensitivity (the limits of detection for ractopamine and Salmonella are 8.1 pg/mL and 20 cfu/mL, respectively). This Mn-mediated magnetic immunosensor not only retains the good stability but also greatly improves the sensitivity of conventional paramagnetic ion-mediated magnetic sensors, offering a promising platform for sensitive, stable, and convenient bioanalysis.

Sensitive CVG-AFS/ICP-MS label-free nucleic acid and protein assays based on a selective cation exchange reaction and simple filtration separation

Nowadays, label-free atomic spectrometric bioassays are attracting great research interest because of their advantages of low cost, simple design and operation, etc. Herein, a novel and simple chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS)/inductively coupled plasma-mass spectrometry (ICP-MS) label-free detection method is presented for highly sensitive and selective assay of DNA and proteins. This work mainly combined a phenomenon that CdTe quantum dots (QDs) can be used to selectively differentiate free Hg2+ and the T-Hg2+-T complex, with the use of simple membrane filtration separation to improve the performance of the label-free bioassay methods. Upon hybridization with the DNA/protein (carcinoembryonic antigen, CEA) target, the T-Hg2+-T hairpin structure was opened and Hg2+ was released; this initiated the cation exchange reaction between Hg2+ and CdTe QDs which released Cd2+ simultaneously. Subsequently, the free Cd2+ was separated by the filtration membrane without separating the CdTe QDs, which could then be separated from the sample matrices for the CVG-AFS/ICP-MS assay. Under the optimal conditions, this method possessed high sensitivity for DNA and CEA determination with limits of detection (LODs) of 0.2 nM and 0.2 ng mL-1, and linear dynamic ranges of 1-160 nM and 0.5-20 ng mL-1, respectively, and exhibited excellent DNA sequence specificity and protein selectivity. This method preserves the advantages of the label-free atomic spectrometric bioassay, and combined with the selective cation exchange reaction and simple filtration separation to improve the performance.

Fe-T1 Sensor Based on Coordination Chemistry for Sensitive and Versatile Bioanalysis

The main challenge of paramagnetic ions-mediated magnetic sensors is their relatively low sensitivity. In this study, we observe the amplification of longitudinal relaxation time (T₁) signal when Fe²⁺ transforms into Fe³⁺ followed by the coordination of potassium thiocyanate (KSCN) and develop a sensitive Fe-T₁ sensor based on the coordination chemistry between KSCN and Fe³⁺ to amplify the T₁ signal for detecting a series of targets, such as hydrogen peroxide, glucose, and antigen/antibody. We justify the practicability of our assay by successfully detecting tetracycline in milk samples and hepatitis C virus in clinical samples with satisfactory accuracy. This KSCN-mediated Fe-T₁ sensor not only realizes biochemical analysis and immunoassay with higher sensitivity but also retains many advantages of paramagnetic ions-mediated magnetic sensors (good stability and straightforward operation), which holds great promise for the detection of a range of targets of interest in complex samples.