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

We report a versatile analytical platform for assaying multiple analytes relying on changes in longitudinal relaxation time (T1) as a result of Fe3+/Fe2+ interconversion. The T1 of water protons in Fe3+ aqueous solution differs significantly from that of Fe2+, allowing for the development of a generally applicable T1-based assay since many redox reactions enable the interconversion between Fe2+ and Fe3+ that can result in the change of T1. Compared with conventional magnetic biosensors, this T1-based assay is free of magnetic nanoparticles (MNPs), and the stability of T1-based assay is better than conventional magnetic sensors that suffer from nonspecific adsorption and aggregation of MNPs. This T1-based assay simultaneously enables "one-step mixing" assays (such as saliva sugar) and "multiple-washing" immunoassays with good stability and sensitivity, offering a promising platform for convenient, stable, and versatile biomedical analysis.

Cu-T1 Sensor for Versatile Analysis.

Conventional magnetic sensors usually employ Fe-based magnetic materials as signal probes. In this work, we find that Cu(II) is also a useful longitudinal relaxation time (T1) signal-based magnetic probe. We adopt bathocuproinedisulfonic acid disodium salt hydrate (BCS) to chelate Cu(I) and form a stable Cu(I)-BCS complex in aqueous solution and find the significant difference in the T1 value of water protons between Cu(II) aqueous solution and Cu(I)-BCS complex aqueous solution. Redox reaction can convert Cu(II) to Cu(I) followed by the complexation of BCS, which results in apparent change of T1 that can serve as magnetic signal readout, which is the basis of this Cu-T1 sensor. Many redox reactions between Cu(II) and Cu(I) allow this Cu-T1 sensor to not only realize "one-step mode" assay such as ascorbic acid, protein, and alkaline phosphatase but also enable "multi-step mode" immunoassay, such as biomacromolecules and small molecules. This Cu-T1 sensor employs Cu ion as signal readout, providing an alternative tool for biochemical analysis.

Cascade Reaction-Mediated Assembly of Magnetic/Silver Nanoparticles for Amplified Magnetic Biosensing.

Conventional magnetic relaxation switching (MRS) sensor suffers from its relatively low sensitivity when it comes to the analysis of trace small molecules in complicated samples. To meet this challenge, we develop a cascade reaction-mediated magnetic relaxation switching (CR-MRS) sensor, based on the assembly of silver nanoparticles (Ag NPs) and magnetic nanoparticles (MNPs) to improve the sensitivity of conventional MRS. The cascade reaction triggered by alkaline phosphatase generates ascorbic acid, which reduces Ag+ to Ag NPs that can assemble the initially dispersed MNPs to form magnetic/silver nanoassemblies, thus modulating the state of MNPs to result in the change of transverse relaxation time. The formed magnetic/silver nanoassemblies can greatly enhance the state change of MNPs (from dispersed to aggregated) and dramatically improve the sensitivity of traditional MRS sensor, which makes this CR-MRS sensor a promising platform for highly sensitive detection of small molecules in complicated samples.

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.

T1-Mediated Nanosensor for Immunoassay Based on an Activatable MnO2 Nanoassembly.

Current magnetic relaxation switching (MRS) sensors for detection of trace targets in complex samples still suffer from limitations in terms of relatively low sensitivity and poor stability. To meet this challenge, we develop a longitudinal relaxation time (T1)-based nanosensor by using Mn2+ released from the reduction of a MnO2 nanoassembly that can induce the change of T1, and thus can greatly improve the sensitivity and overcome the "hook effect" of conventional MRS. Through the specific interaction between antigen and the antibody-functionalized MnO2 nanoassembly, the T1 signal of Mn2+ released from the nanoassembly is quantitatively determined by the antigen, which allows for highly sensitive and straightforward detection of targets. This approach broadens the applicability of magnetic biosensors and has great potential for applications in early diagnosis of disease biomarkers.

Peptide-Mediated Controllable Cross-Linking of Gold Nanoparticles for Immunoassays with Tunable Detection Range.

The colorimetric immunoassay based on gold nanoparticles (AuNPs) can hardly enable simultaneous detection of multiple biomarkers in vastly different concentrations (e.g., pg/mL-µg/mL) because of its narrow dynamic range. In this work, we demonstrate an immunoassay with tunable detection range by using peptide-mediated controlled aggregation of surface modification-free AuNPs. Alkaline phosphatase (ALP) removes the phosphate group of the peptide to yield a positively charged product, which triggers the aggregation of negatively charged AuNPs and the color change of the AuNPs solution from red to blue with naked-eye readout. We design and screen 20 kinds of phosphorylated peptides to obtain a broad and controllable detection range for ALP sensing and apply them for detecting multiple inflammatory biomarkers in clinical samples. Our assay realizes straightforward, multiplexed, and simultaneous detection of multiple clinical biomarkers with tunable detection range (from pg/mL to µg/mL) in the same run and holds great potential for chemical/biochemical analysis.

Bioorthogonal Reaction-Mediated ELISA Using Peroxide Test Strip as Signal Readout for Point-of-Care Testing.

This work demonstrates a highly sensitive peroxide test strip (PTS)-based enzyme-linked immunosorbent assay (ELISA) for both qualitative and quantitative detection of drugs of abuse (morphine) and disease biomarkers (interleukin-6 and HIV-1 capsid antigen p24). This color-based PTS is a commercially available product with advantages of low cost, easy operation, and portability, and it is an ideal signal readout strategy in ELISA to simplify the immunoassay procedures and enable point-of-care testing (POCT). In addition, we introduce the bioorthogonal reaction that can effectively amplify the signal by controlling the cycles of bioorthogonal reaction to achieve the desirable sensitivity depending on different analytes. The limit of detection is 0.2 ng/mL for morphine, 3.98 pg/mL for interleukin-6, and 11.6 pg/mL for detection of HIV-capsid antigen (p24). This PTS-ELISA applies to both the qualitative and quantitative detection of IL-6 and p24 in clinical serum samples with good accuracy, which provides a promising tool for the POCT in clinical diagnosis.

Double-Enzymes-Mediated Bioluminescent Sensor for Quantitative and Ultrasensitive Point-of-Care Testing.

We report an ultrasensitive, quantitative, and rapid bioluminescent immunosensor (ABS) for point-of-care testing (POCT) of the disease biomarker in clinical samples using double enzymes including alkaline phosphatase (ALP) and luciferase. In the presence of the biomarker, the ALP attached on the surface of immuno-nanocomplex dephosphorylates adenine triphosphate (ATP), subsequently inhibiting the ATP-luciferin-luciferase bioluminescent reaction. The highly sensitive response of ATP (picomolar level) allows for ultrasensitive detection of biomarker via the effective change of the bioluminescence intensity through ALP- and luciferase-catalyzed reactions, which can be quantitatively determined by a portable ATP detector. This ABS fulfills the criteria for POCT that performs sensitive (femtomolar level of biomarkers) and quantitative measurement quickly (less than 1 h) with minimal equipment (portable detector).

An enzyme-mediated competitive colorimetric sensor based on Au@Ag bimetallic nanoparticles for highly sensitive detection of disease biomarkers.

We developed a competitive colorimetric nanosensor based on Au@Ag bimetallic nanoparticles for the detection of interleukin-6 (IL-6) in clinical samples. Antibody-conjugated magnetic nanoparticles (MNPs) and polystyrene (PS) microparticles conjugated with both catalase and a secondary antibody can form sandwich structures that enable one-step target enrichment and separation. The catalase on the surface of the PS can catalyze the hydrolysis of hydrogen peroxide (H2O2) to regulate the deposition of Ag+ on the surface of gold nanoparticles (AuNPs), and forms different sizes and amounts of Au@Ag bimetallic nanoparticles (Au@AgNPs) which produce a distinct color signal for readout with the naked eye. Our sensor features high sensitivity, selectivity, reproducibility and anti-interference property as a result of comprehensive parameter optimization. The limit of detection of IL-6 can reach 11 pg mL-1 with the naked eye and 1.2 pg mL-1 by quantitative instrumental analysis. The whole analysis can be finished within 1 h. More importantly, we successfully apply our platform or the detection of IL-6 in clinical samples with better accuracy than conventional enzyme-linked immunosorbent assay (ELISA).

Magnetic Lateral Flow Strip for the Detection of Cocaine in Urine by Naked Eyes and Smart Phone Camera.

Magnetic lateral flow strip (MLFS) based on magnetic bead (MB) and smart phone camera has been developed for quantitative detection of cocaine (CC) in urine samples. CC and CC-bovine serum albumin (CC-BSA) could competitively react with MB-antibody (MB-Ab) of CC on the surface of test line of MLFS. The color of MB-Ab conjugate on the test line relates to the concentration of target in the competition immunoassay format, which can be used as a visual signal. Furthermore, the color density of the MB-Ab conjugate can be transferred into digital signal (gray value) by a smart phone, which can be used as a quantitative signal. The linear detection range for CC is 5-500 ng/mL and the relative standard deviations are under 10%. The visual limit of detection was 5 ng/mL and the whole analysis time was within 10 min. The MLFS has been successfully employed for the detection of CC in urine samples without sample pre-treatment and the result is also agreed to that of enzyme-linked immunosorbent assay (ELISA). With the popularization of smart phone cameras, the MLFS has large potential in the detection of drug residues in virtue of its stability, speediness, and low-cost.

Reversible Photoinduced Switching of Permeability in a Cast Non-Porous Film Comprising Azobenzene Liquid Crystalline Polymer.

Permeation characteristics of an azobenzene-containing liquid crystalline (LC) non-porous film are investigated using a metallic corrosion method. Thin films (300 nm) are fabricated by the solution casting of an azobenzene side-chain LC polymer on freshly polished carbon steel coupons. Coated coupons are treated under the following conditions: a) gradual annealing at a cooling rate lower than 1 °C · min(-1) from 150 °C (above its Tg ) to room temperature, and b) irradiation at 465 nm (20 mW · cm(-2) ) with either circularly polarized light (CPL) or non-polarized light (NPL). The morphology of these films is characterized using X-ray diffraction, polarized optical microscopy, and transmission measurements. The results suggest that the annealing treatment resulted in the formation of a polydomain structure consisting of locally ordered small smectic domains that lack mutual orientation. Ordered micro domains are surrounded by disordered phases. CPL and NPL irradiation generates a monodomain orientated structure and an isotropic liquid crystal glass, respectively. The permeability of these non-porous films treated by CPL, NPL, and annealing are found to be 6.14 × 10(-4) , 1.92 × 10(-2) , and 1.56 × 10(-3) cm(3) · m(-2) · d(-1) . An orientation-dependent structure model is constructed to explain the permeation phenomenon, considering the ordered phase is impermeable, only the disordered phase is accessible to penetrating molecules. Fast switching of gas permeation is demonstrated by alternative irradiation of the film with CPL and NPL, which results in an approximately 30-fold difference in the permeability of the non-porous film.

"One-for-All"-Type, Biodegradable Prussian Blue/Manganese Dioxide Hybrid Nanocrystal for Trimodal Imaging-Guided Photothermal Therapy and Oxygen Regulation of Breast Cancer.

Multimodal imaging-guided diagnosis and therapy has been highlighted in the area of theranostic nanomaterials. To provide more suitable theranostic candidates, Prussian blue (PB)/manganese dioxide (MnO2) hybrid nanoparticles (PBMn) smaller than 50 nm are prepared by a one-pot method. MnO2, which is reduced from KMnO4, not only controls the particle size, the optical properties, and the transverse relaxation rate (r2) of PB but also enhances the catalysis efficacy of PB to H2O2 for oxygen generation. PBMn can serve as a photoacoustic imaging (PAI) and longitudinal relaxation (T1) mode magnetic resonance imaging contrast agent (14 times and 1.8 times of the saline-treated group, respectively). Injection of PBMn can regulate the oxygen partial pressure of the tumor tissue from 2.1 ± 0.2 to 9.3 ± 0.4 kPa and rearrange the ratio of oxygenated hemoglobin and deoxygenate hemoglobin inside the tumor, which favor the enhancement of the diamagnetic T2-weighted imaging (T2WI) signal intensity (two times that of the saline-treated group). Furthermore, PBMn-mediated PTT can efficiently inhibit the growth of the MCF-7 tumor in vitro and in vivo. PBMn can serve as a PAI/T1/T2 trimodal contrast agent and in imaging-guided PTT, as well as in the oxygen regulation of the exografted breast cancer.

Novel Approach of Using Near-Infrared Responsive PEGylated Gold Nanorod Coated Poly(l-lactide) Microneedles to Enhance the Antitumor Efficiency of Docetaxel-Loaded MPEG-PDLLA Micelles for Treating an A431 Tumor.

The combination of chemotherapy and photothermal therapy (PTT) plays a significant role in synergistic tumor therapy. However, a high dosage of chemotherapy drugs or photothermal agents may cause series side effects. To overcome these challenges, we designed a near-infrared (NIR) responsive PEGylated gold nanorod (GNR-PEG) coated poly(l-lactide) microneedle (PLLA MN) system (GNR-PEG@MN) to enhance antitumor efficiency of docetaxel-loaded MPEG-PDLLA (MPEG-PDLLA-DTX) micelles for treating an A431 tumor. The as-made GNR-PEG@MNs contained only 31.83 ± 1.22 µg of GNR-PEG per patch and exhibited excellent heating efficacy both in vitro and in vivo. Meanwhile, GNR-PEG@MN with the height of 480 µm had good skin insertion ability and was harmless to the skin. On the other hand, GNR-PEG@MN had good heating transfer ability in vivo, and the tumor sites could reach 50 °C within 5 min. In comparison with chemotherapy and PTT alone, the combination of low dosage MPEG-PDLLA-DTX micelles (5 mg/kg) and GNR-PEG@MNs completely eradicated the A431 tumor without recurrence in vivo, demonstrating a remarkable synergetic effect. Hence, GNR-PEG@MN could be a promising carrier to enhance the antitumor effect of MPEG-PDLLA-DTX micelles for treating superficial tumors and is expected to have a great potential in clinical translation for human epidermoid cancer therapy.

One-step multiplexed detection of foodborne pathogens: Combining a quantum dot-mediated reverse assaying strategy and magnetic separation.

A rapid and multiplexed immunosensor was developed based on a quantum dot (QD)-reverse assaying strategy (RAS) and immuno-magnetic beads (IMBs) for one-step and simultaneous detection of Escherichia coli O157: H7 and Salmonella. In a conventional QD-based immunosensor, the fluorescence signal of the "IMBs-target-QD" immunoconjugate is directly used as the assaying readout. However, the fluorescence signal is affected by IMBs due to light scattering and the "IMBs-target-QD" immunoconjugate needs multiple washing and re-suspension steps. To address these problems, we use the surplus QD-antibody conjugate as signal readout in the RAS, which prevents interference from the IMBs, increases the fluorescence signal, and avoids complex operations. Compared with conventional QD-based immunosensor, the sensitivity of QD-RSA immunosensor for detection of Escherichia coli O157: H7 has been improved fifty-fold, and whole analysis procedure can be finished within 1h. Therefore, this RSA strategy is promising for improving the performance of QD-based immunosensors and could greatly broaden their applications.

Tumor-targeted paclitaxel delivery and enhanced penetration using TAT-decorated liposomes comprising redox-responsive poly(ethylene glycol).

To combine the advantage of poly(ethylene gylcol) (PEG) for longer circulation and cell-penetrating peptides (CPPs) for efficient cellular uptake, paclitaxel (PTX)-loaded liposomes functionalized with TAT, the most frequently used CPP, and cleavable PEG via a redox-responsive disulfide linker (PTX-C-TAT-LP) were successfully developed here. Under physiological conditions, TAT was shielded by PEG layer and liposomes exhibited a long blood circulation. At tumor site, PEG could be detached in the presence of exogenous reducing agent [glutathione (GSH)] and TAT was exposed to facilitate cell internalization. In the presence of GSH, the liposomal vesicle C-TAT-LP showed increased cellular uptake and improved three-dimensional tumor spheroids penetration in vitro compared with analogous stable shielded liposomes. C-TAT-LP achieved enhanced tumor distribution and demonstrated superior delivery efficiency in vivo. PTX-C-TAT-LP with GSH strongly inhibited the proliferation of murine melanoma B16F1 tumor cells in vitro and in vivo with the tumor inhibition rate being 69.4% on B16F1-bearing mice. In addition, the serum aspartate transaminase level, alanine transaminase level, and creatine kinase level were almost completely within normal range in the PTX-C-TAT-LP with GSH group, revealing PTX-C-TAT-LP with GSH had no obvious drug-related adverse events for liver and heart. Taken together, C-TAT-LP is a promising tumor-targeting drug carrier.