Shasha Jia

Target-Responsive "Sweet" Hydrogel with Glucometer Readout for Portable and Quantitative Detection of Non-Glucose Targets

Portable devices with the advantages of rapid, on-site, user-friendly, and cost-effective assessment are widely applied in daily life. However, only a limited number of quantitative portable devices are commercially available, among which the personal glucose meter (PGM) is the most successful example and has been the most widely used. However, PGMs can detect only blood glucose as the unique target. Here we describe a novel design that combines a glucoamylase-trapped aptamer-cross-linked hydrogel with a PGM for portable and quantitative detection of non-glucose targets. Upon target introduction, the hydrogel collapses to release glucoamylase, which catalyzes the hydrolysis of amylose to produce a large amount of glucose for quantitative readout by the PGM. With the advantages of low cost, rapidity, portability, and ease of use, the method reported here has the potential to be used by the public for portable and quantitative detection of a wide range of non-glucose targets.

Au@Pt Nanoparticle Encapsulated Target‐Responsive Hydrogel with Volumetric Bar‐Chart Chip Readout for Quantitative Point‐of‐Care Testing

Point-of-care testing (POCT) with the advantages of speed, simplicity, portability, and low cost is critical for the measurement of analytes in a variety of environments where access to laboratory infrastructure is lacking. While qualitative POCTs are widely available, quantitative POCTs present significant challenges. Here we describe a novel method that integrates an Au core/Pt shell nanoparticle (Au@PtNP) encapsulated target-responsive hydrogel with a volumetric bar-chart chip (V-Chip) for quantitative POCT. Upon target introduction, the hydrogel immediately dissolves and releases Au@PtNPs, which can efficiently catalyze the decomposition of H2 O2 to generate a large volume of O2 to move of an ink bar in the V-Chip. The concentration of the target introduced can be visually quantified by reading the traveling distance of the ink bar. This method has the potential to be used for portable and quantitative detection of a wide range of targets without any external instrument.

Translating Molecular Recognition into a Pressure Signal to enable Rapid, Sensitive, and Portable Biomedical Analysis

Herein, we demonstrate that a very familiar, yet underutilized, physical parameter—gas pressure—can serve as signal readout for highly sensitive bioanalysis. Integration of a catalyzed gas-generation reaction with a molecular recognition component leads to significant pressure changes, which can be measured with high sensitivity using a low-cost and portable pressure meter. This new signaling strategy opens up a new way for simple, portable, yet highly sensitive biomedical analysis in a variety of settings.

Design and Synthesis of Target-Responsive Aptamer-Cross-linked Hydrogel for Visual Quantitative Detection of Ochratoxin A

A target-responsive aptamer-cross-linked hydrogel was designed and synthesized for portable and visual quantitative detection of the toxin Ochratoxin A (OTA), which occurs in food and beverages. The hydrogel network forms by hybridization between one designed DNA strand containing the OTA aptamer and two complementary DNA strands grafting on linear polyacrylamide chains. Upon the introduction of OTA, the aptamer binds with OTA, leading to the dissociation of the hydrogel, followed by release of the preloaded gold nanoparticles (AuNPs), which can be observed by the naked eye. To enable sensitive visual and quantitative detection, we encapsulated Au@Pt core-shell nanoparticles (Au@PtNPs) in the hydrogel to generate quantitative readout in a volumetric bar-chart chip (V-Chip). In the V-Chip, Au@PtNPs catalyzes the oxidation of H2O2 to generate O2, which induces movement of an ink bar to a concentration-dependent distance for visual quantitative readout. Furthermore, to improve the detection limit in complex real samples, we introduced an immunoaffinity column (IAC) of OTA to enrich OTA from beer. After the enrichment, as low as 1.27 nM (0.51 ppb) OTA can be detected by the V-Chip, which satisfies the test requirement (2.0 ppb) by the European Commission. The integration of a target-responsive hydrogel with portable enrichment by IAC, as well as signal amplification and quantitative readout by a simple microfluidic device, offers a new method for portable detection of food safety hazard toxin OTA.

A cell-surface-anchored ratiometric fluorescent probe for extracellular pH sensing

Accurate sensing of the extracellular pH is a very important yet challenging task in biological and clinical applications. This paper describes the development of an amphiphilic lipid-DNA molecule as a simple yet useful cell-surface-anchored ratiometric fluorescent probe for extracellular pH sensing. The lipid-DNA probe, which consists of a hydrophobic diacyllipid tail and a hydrophilic DNA strand, is modified with two fluorescent dyes; one is pH-sensitive as pH indicator and the other is pH-insensitive as an internal reference. The lipid-DNA probe showed sensitive and reversible response to pH change in the range of 6.0-8.0, which is suitable for most extracellular studies. In addition, based on simple hydrophobic interactions with the cell membrane, the lipid-DNA probe can be easily anchored on the cell surface with negligible cytotoxicity, excellent stability, and unique ratiometric readout, thus ensuring its accurate sensing of extracellular pH. Finally, this lipid-DNA-based ratiometric pH indicator was successfully used for extracellular pH sensing of cells in 3D culture environment, demonstrating the potential applications of the sensor in biological and medical studies.

Integration of target responsive hydrogel with cascaded enzymatic reactions and microfluidic paper-based analytic devices (µPADs) for point-of-care testing (POCT).

Paper based microfluidics (µPADs) with advantages of portability, low cost, and ease of use have attracted extensive attention. Here we describe a novel method that integrates glucoamylase-trapped aptamer-crosslinked hydrogel for molecular recognition with cascaded enzymatic reactions for signal amplification and a µPAD for portable readout. Upon target introduction, the hydrogel decomposes to release glucoamylase, which catalyzes the hydrolysis of amylose to produce a large amount of glucose. With a simple folding of the µPAD, the sample solution containing glucose product wicks and diffuses in parallel to each test-zone to carry out homogeneous assays, where glucose is used to produce I2 for brown color visualization through multiple enzymatic and chemical cascade reactions. Through color gradient changes based on different concentrations of the target, a semiquantitative assay is achieved by the naked eye, and quantitation can be obtained by handheld devices. Detection of cocaine in buffer and urine was performed to demonstrate the utility of the hydrogel-µPAD system. More importantly, the hydrogel-µPAD system can be extended to the detection of various targets by incorporating the corresponding aptamer into the hydrogel. The hydrogel-µPAD system reported here provides a new platform for portable, disposable and visual detection of a wide range of targets.

Microfluidic approaches to rapid and efficient aptamer selection

With their advantages as molecular recognition elements, aptamers have been extensively studied and used for bioanalytical and biomedical applications. However, the process of enrichment and screening of aptamers remains a bottleneck for aptamer development. Recently, microfluidic methods have been increasingly used for rapid and efficient aptamer selection, showing their remarkable advantages over conventional methods. This review briefly introduces aptamers and their advantages. The conventional process of generating aptamers is discussed, followed by the analysis of the key obstacles to efficient aptamer selection. Microfluidic methods for highly efficient enrichment and screening of aptamers are reviewed in detail.

Synergetic Approach for Simple and Rapid Conjugation of Gold Nanoparticles with Oligonucleotides

Attaching thiolated DNA on gold nanoparticles (AuNPs) has been extremely important in nanobiotechnology because DNA-AuNPs combine the programmability and molecular recognition properties of the biopolymers with the optical, thermal, and catalytic properties of the inorganic nanomaterials. However, current standard protocols to attach thiolated DNA on AuNPs involve time-consuming, tedious steps and do not perform well for large AuNPs, thereby greatly restricting applications of DNA-AuNPs. Here we demonstrate a rapid and facile strategy to attach thiolated DNA on AuNPs based on the excellent stabilization effect of mPEG-SH on AuNPs. AuNPs are first protected by mPEG-SH in the presence of Tween 20, which results in excellent stability of AuNPs in high ionic strength environments and extreme pHs. A high concentration of NaCl can be applied to the mixture of DNA and AuNP directly, allowing highly efficient DNA attachment to the AuNP surface by minimizing electrostatic repulsion. The entire DNA loading process can be completed in 1.5 h with only a few simple steps. DNA-loaded AuNPs are stable for more than 2 weeks at room temperature, and they can precisely hybridize with the complementary sequence, which was applied to prepare core-satellite nanostructures. Moreover, cytotoxicity assay confirmed that the DNA-AuNPs synthesized by this method exhibit lower cytotoxicity than those prepared by current standard methods. The proposed method provides a new way to stabilize AuNPs for rapid and facile loading thiolated DNA on AuNPs and will find wide applications in many areas requiring DNA-AuNPs, including diagnosis, therapy, and imaging.

Simple and Rapid Functionalization of Gold Nanorods with Oligonucleotides Using an mPEG-SH/Tween 20-Assisted Approach

DNA conjugated gold nanorods (AuNRs) are widely applied for nanostructure assembly, gene therapy, biosensing, and drug delivery. However, it is still a great challenge to attach thiolated DNA on AuNRs, because the positively charged AuNRs readily aggregate in the presence of negatively charged DNA. This article reports an mPEG-SH/Tween 20-assisted method to load thiolated DNA on AuNRs in 1 h. Tween 20 and mPEG-SH are used to synergistically displace CTAB on the surface of AuNRs by repeated centrifugation and resuspension, and thiolated DNA are attached to AuNRs in the presence of 1 M NaCl, 100 mM MgCl2, or 100 mM citrate. AuNRs with different sizes and aspect ratios can be functionalized with DNA by this method. The number of DNA loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20 or the ratio between DNA and AuNR. Functionalized AuNRs were used for nanoparticle assembly and cancer cell imaging to confirm that DNA anchored on the surface of AuNRs retains its hybridization and molecular recognition capability. The new method is easy, rapid, and robust for the preparation of DNA functionalized AuNRs for a variety of applications such as cancer therapy, drug delivery, self-assembly, and imaging.

Facile and rapid generation of large-scale microcollagen gel array for long-term single-cell 3D culture and cell proliferation heterogeneity analysis.

Microfabricated devices are suitable for single-cell analysis due to their high throughput, compatible dimensions and controllable microenvironment. However, existing devices for single-cell culture and analysis encounter some limitations, such as nutrient depletion, random cell migration and complicated fluid shear influence. Moreover, most of the single-cell culture and analysis devices are based on 2D cell culture conditions, even though 3D cell culture methods have been demonstrated to better mimic the real cell microenvironment in vivo. To solve these problems, herein we develop a microcollagen gel array (μCGA) based approach for high-throughput long-term single-cell culture and single-cell analysis under 3D culture conditions. Type-I collagen, a well-established 3D cell culture medium, was used as the scaffold for 3D cell growth. A 2 × 2 cm PDMS chip with 10 000 μCGA units was fabricated to encapsulate thousands of single cells in less than 15 min. Single cells were able to be confined and survive in μCGA units for more than 1 month. The capability of large-scale and long-term single-cell 3D culture under open culture conditions allows us to study cellular proliferation heterogeneity and drug cytotoxicity at the single-cell level. Compared with existing devices for single-cell analysis, μCGA solves the problems of nutrient depletion and random cellular migration, avoids the influence of complicated fluid shear, and mimics the real 3D growth environment in vivo, thereby providing a feasible 3D long-term single-cell culture method for single-cell analysis and drug screening.