Magnetic bead-liposome hybrids enable sensitive and portable detection of DNA methyltransferase activity using personal glucose meter

Nanometer-Sized Boron Loaded Liposomes Containing Fe3O4 Magnetic Nanoparticles and Tributyl Borate and Anti-Albumin from Bovine Serum Antibody for Thermal Neutron Detection

A shortage in the supply of ³He used for thermal neutron detector makes researchers to find ³He alternatives for developing new neutron detectors. Here, we prepared a neutron-sensitive composite liposome with tributyl borate and encapsulating with Fe₃O₄@oleic acid nanoparticles (Fe₃O₄@OA NPs), methylene blue (MB), or anti-albumin from bovine serum (anti-BSA). The tributyl borate compound was characterized by Fourier transform infrared spectroscopy (FT-IR). In addition, the morphology, element compositions, and magnetic properties of the composite liposome were investigated with transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and vibrating sample magnetometer (VSM), respectively. The results indicated that a typical ellipsoidal magnetic liposome structure was obtained, and the lengths of the minor axis and major axis were 49 ± 1 nm and 87 ± 3 nm, respectively. Under thermal neutron irradiation, the structure of composite liposome was destroyed, and encapsulated reporter molecules were released, which was detected by ultraviolet–visible (UV–vis) spectroscopy and surface plasmon resonance (SPR) technology. The response of this sensor based on a destructive assay shows a good correlation with neutron doses. Besides, the sensor has a neutron to gamma-ray rejection ratio of 1568 at a thermal neutron flux rate of 135.6 n/cm²·s, which makes it a promising alternative to ³He.

Fast Screening of Biomembrane-Permeable Compounds in Herbal Medicines Using Bubble-Generating Magnetic Liposomes Coupled with LC-MS

A novel strategy based on the use of bionic membrane camouflaged magnetic particles and LC–MS was developed to quickly screen the biomembrane-permeable compounds in herbal medicines. The bionic membrane was constructed by bubble-generating magnetic liposomes loaded with NH₄HCO₃ (BMLs). The lipid bilayer structure of the liposomes enabled BMLs to capture biomembrane-permeable compounds from a herbal extract. The BMLs carrying the compounds were then separated from the extract by a magnetic field. Upon heat treatment, NH₄HCO₃ rapidly decomposed to form CO₂ bubbles within the liposomal bilayer, and the captured compounds were released from BMLs and analyzed by LC–MS. Jinlingzi San (JLZS), which contains various natural ingredients, was chosen to assess the feasibility of the proposed method. As a result, nine potential permeable compounds captured by BMLs were identified for the first time. Moreover, an in vivo animal study found that most of the compounds screened out by the proposed method were absorbed into the blood. The study provides a powerful tool for rapid and simultaneous prediction of multiple biomembrane-permeable components.

DNAzyme Amplified Aptasensing Platform for Ochratoxin A Detection Using a Personal Glucose Meter

Aptamer-based sensors have emerged as a major platform for detecting small-molecular targets, because aptamers can be selected to bind these small molecules with higher affinity and selectivity than other receptors such as antibodies. However, portable, accurate, sensitive, and affordable detection of these targets remains a challenge. In this work, we developed an aptasensing platform incorporating magnetic beads and a DNAzyme for signal amplification, resulting in high sensitivity. The biosensing platform was constructed by conjugating a biotin-labeled aptamer probe of small-molecular targets such as toxins and a biotin-labeled substrate strand on magnetic beads, and the DNAzyme strand hybridized with the aptamer probe to block the substrate cleavage activity. The specific binding of the small-molecular target by the aptamer probe can replace the DNAzyme strand and then induce the hybridization between the DNAzyme strand and substrate strand, and the iterative signal amplification reaction of hydrolysis and cleavage of the substrate chain occurs in the presence of a metal ion cofactor. Using invertase to label the substrate strand, the detection of small molecules of the toxin is successfully transformed into the measurement of glucose, and the sensitive analysis of small molecules such as toxins can be realized by using the household portable glucose meter as a readout. This platform is shown to detect ochratoxin, a common toxin in food, with a linear detection range of 5 orders of magnitude, a low detection limit of 0.88 pg/mL, and good selectivity. The platform is easy to operate and can be used as a potential choice for quantitative analysis of small molecules, at home or under point-of-care settings. Moreover, by changing and designing the aptamer probe and the arm of DNAzyme strand, it can be used for the analysis of other analytes.

Catalytic hairpin assembly mediated liposome-encoded magnetic beads for signal amplification of peroxide test strip based point-of-care testing of ricin

Herein, we propose a new peroxide test strip (PTS) based point-of-care testing (POCT) method to detect ricin B-chain qualitatively and quantitatively by using catalytic hairpin assembly (CHA) mediated liposome-encoded magnetic beads for signal amplification. The sensitivity of this PTS based POCT method was improved significantly because it combined CHA signal amplification and liposome-based signal amplification.

Magnetic bead-enzyme assemble for triple-parameter telomerase detection at single-cell level

In this work, we developed a triple-parameter strategy for the detection of telomerase activity from cancer cells and urine samples. This strategy was developed based on magnetic bead-enzyme hybrids combined with fluorescence analysis, colorimetric assay, or adenosine triphosphate (ATP) meter as readout. The application of magnetic bead-enzyme hybrids has the advantages of magnetic separation and signal amplification. These detection methods can be used individually or in combination to achieve the optimal sensing performance and make the results more convincing. Among them, the ATP meter with portable size had easy operation and low cost, and this response strategy provided a higher sensitivity at the single-cell level. The designed strategy was suitable as naked-eye sensor and point-of-care testing (POCT) for rapid assaying of telomerase activity. Graphical abstract Magnetic bead-enzyme assemble for triple-parameter telomerase detection.

Translating in vitro diagnostics from centralized laboratories to point-of-care locations using commercially-available handheld meters

There is a growing demand for high-performance point-of-care (POC) diagnostic technologies where in vitro diagnostics (IVD) is fundamental for prevention, identification, and treatment of many diseases. Over the past decade, a shift of IVDs from the centralized laboratories to POC settings is emerging. In this review, we summarize recent progress in translating IVDs from centralized labs to POC settings using commercially available handheld meters. After introducing typical workflows for IVDs and highlight innovative technologies in this area, we discuss advantages of using commercially available handheld meters for translating IVDs from centralized labs to POC settings. We then provide comprehensive coverage of different signal transduction strategies to repurpose the commercially-available handheld meters, including personal glucose meter, pH meter, thermometer and pressure meter, for detecting a wide range of targets by integrating biochemical assays with the meters for POC testing. Finally, we identify remaining challenges and offer future outlook in this area.

A dandelion-like liposomes-encoded magnetic bead probe-based toehold-mediated DNA circuit for the amplification detection of MiRNA

The development of facile and sensitive miRNA quantitative detection methods is a central challenge for the early diagnosis of miRNA-related diseases. Herein, we propose a strategy for a liposome-encoded magnetic bead-based DNA toehold-mediated DNA circuit for the simple and sensitive detection of miRNA based on a toehold-mediated circular strand displacement reaction (TCSDR) coupled with a personal glucometer (PGM ). In this strategy, a glucoamylase-encapsulated liposomes (GELs)-encoded magnetic bead (GELs-MB) probe is designed to integrate target binding, magnetic separation, and signal response. Upon sensing the target miRNA-21, a GELs-MB probe-based toehold-mediated circular strand displacement reaction (TCSDR) was initiated with the help of fuel-DNA, constructing a DNA circuit system, and realizing target recycling amplification and the disassembly of the liposomes. The disassembled liposomes were finally removed via magnetic separation, and the encapsulated glucoamylase was liberated to catalyze amylose hydrolysis with multiple turnovers to glucose for a PGM readout. Benefiting from target recycling amplification initiated by the toehold-mediated DNA circuit and the liposome multiple-label amplification, a small quantity of target miRNA-21 can be transformed into a large glucose signal. The strategy realized the quantification of miRNA-21 down to a level of 0.7 fM without enzymatic amplification or precise instrumentation. Moreover, the high-density GELs-MB probe allows the sensitive detection of miRNA-21 to be accomplished within 1.5 h. Furthermore, this strategy exhibits the advantages of specificity and simplicity, since a toehold-mediated strand displacement reaction, magnetic separation and portable PGM were used. Importantly, this strategy has been demonstrated to allow the high-confidence quantification of miRNA. Therefore, with the advantages of low cost, ease of use, portability, and sensitivity, the reported method holds great potential for the early diagnosis of miRNA-related diseases.

Target-controlled liposome amplification for versatile nanopore analysis

We have reported a versatile nanopore method based on the combination of analyte-controlled liposome signal amplification and the nanopore detection of a reporter molecule, which largely extends the nanopore application range, and easily elevates the nanopore sensitivity to the fM level from the μM level.

Dual-Amplification Strategy-Based SERS Chip for Sensitive and Reproducible Detection of DNA Methyltransferase Activity in Human Serum

Herein, we present a dual-amplification sensing strategy-based surface-enhanced Raman scattering (SERS) chip, which combines rolling circle amplification (RCA) and polyadenine (PolyA) assembly for sensitive and reproducible determination of the activity of M.SssI, a cytosine-guanine dinucleotide (CpG) methyltransferase (MTase). Typically, in the presence of M.SssI, RCA process is triggered, resulting in long, single-stranded DNA (ssDNA) fragments that are hybridized with thousands of Raman reporters of Cy3. Afterward, the resultant ssDNA fragments are conjugated to SERS-active substrates made of silver core-gold satellite nanocomposites-modified silicon wafer (Ag-Au NPs@Si), with the SERS enhancement factor of ∼5 × 10⁶. The core-satellite nanostructures are assembled relied on the strong affinity of PolyA toward gold/silver surface. Of particular significance, the developed SERS chip displays an ultrahigh sensitivity with a low limit of detection (LOD) of 2.8 × 10^-3 U/mL, which is around 2 orders of magnitude higher than most reported methods. In addition, the constructed chip features a broad detection range covering from 0.05 to 50 U/mL. Besides for the ultrahigh sensitivity and broad dynamic range, the chip also features good reproducibility (e.g., the relative standard deviation (RSD) is less than ∼12%). Taking advantages of these merits, the developed chip is feasible for accurate discrimination of M.SssI with various concentrations spiked in human serum samples with good recoveries ranging from 99.6% to 107%.

A sensitive and low background fluorescent sensing strategy based on g-C3N4-MnO2 sandwich nanocomposite and liposome amplification for ricin detection

Ricin is an extremely potent ribosome-inactivating protein and serves as a likely food biocontaminant or biological weapon. Thus, simple, sensitive and accurate analytical assays capable of detecting ricin are urgently needed to be established. Herein, we present a novel method for ricin B-chain (RTB) detection by using two materials: (a) a highly efficient hybrid probe that was formed by linking a glucose oxidase (GOD)-encapsulated liposome (GOD-L) to magnetic beads (MBs) through hybridization between an aptamer and a blocker and (b) a new low-background g-C3N4-MnO2 sandwich nanocomposite that exhibits fluorescence resonance energy transfer (FRET) between the g-C3N4 nanosheet and MnO2. In the presence of RTB, the strong binding between RTB and the aptamer can release the blocker-linked liposome from the surface of the MBs. After magnetic separation, the decomposed liposome can release GOD to catalyze the oxidation of glucose, generating a certain amount of H2O2. Then, H2O2 can reduce MnO2 of the g-C3N4-MnO2 nanocomposite to Mn2+, which leads to the elimination of FRET. Thus, the fluorescence of the g-C3N4 nanosheet will be turned on. Because of the excellent signal amplification ability of liposome and the characteristic highly sensitive response of the g-C3N4-MnO2 nanocomposite toward H2O2, RTB could be detected sensitively based on the significantly enhanced fluorescent intensity. The linear range of detection was from 0.25 μg mL-1 to 50 μg mL-1 and the limit of detection (LOD) was 190 ng mL-1. Moreover, the proposed assay was successfully applied in the detection of the entire ricin toxin content in a castor seed.

A fluorometric aptamer-based assay for ochratoxin A using magnetic separation and a cationic conjugated fluorescent polymer

A fluorometric aptamer-based assay for ochratoxin A (OTA) is described. It is making use of magnetic separation and a cationic conjugated fluorescent polymer. Amino-tagged aptamer (Apt) against OTA is immobilized on magnetic beads (MBs) to form a conjugate of type Apt-MBs. The immobilized aptamer is partially complementary to carboxyfluorescein-labeled DNA which binds to the Apt-MBs via hybridization if OTA is absent. Only few FAM-DNA will remain in the supernatant after magnetic separation, and only weak fluorescence resonance energy transfer (FRET) occurs on addition of the fluorescent polymer. If, however, OTA is present, it will bind to the aptamer and prevent the hybridization between Apt-DNA and FAM-DNA. This results in the presence of large amounts of FAM-DNA in the supernatant after magnetic separation. On addition of fluorescent polymer, efficient FRET occurs from the polymer to FAM-DNA. Fluorescence, best measured at excitation/emission peaks of 370/530 nm, increases with increasing concentrations of OTA. This assay is highly sensitive and selective. The detection limit is as low as 0.11 ng mL^-1. This is 6 times lower than the aptamer assay without using the fluorescent polymer. Conceivably, this method has a wider scope in that it may be extended to other mycotoxins by simply changing the aptamer. Graphical Abstract Schematic of a fluorometric aptamer assay for ochratoxin A (OTA). It is based on magnetic separation coupled with a cationic conjugated polymer (PFP).

Liposome-encoded magnetic beads initiated by padlock exponential rolling circle amplification for portable and accurate quantification of microRNAs

In this work, we propose a strategy for glucoamylase-encapsulated liposome-encoded magnetic beads initiated by padlock exponential rolling circle amplification (P-ERCA) for portable and accurate quantification of miRNA by using a glucometer (GM) for readout.