Fast probing of glucose and fructose in plant tissues via plasmonic affinity sandwich assay with molecularly-imprinted extraction microprobes

Flexible molecularly imprinted glucose sensor based on graphene sponge and Prussian blue

To enhance the sensitivity of flexible glucose sensors made with 3-aminophenylboronic acid and pyrrole as functional molecules and a carbon tri-electrode as substrate, graphene sponge (GS) and Prussian blue (PB) were used to enhance the charge transfer between the molecularly imprinted cavities and the electrodes. Electrochemical impedance spectroscopy and cyclic voltammetry showed that modifying the electrode with GS and PB significantly reduced the charge transfer impedance and increased the redox current of the sensor. The sensor has a sensitivity of up to 25.81 µA⋅loge (µM)-1⋅cm-2 for the detection of glucose using differential pulse voltammetry in the range of 7.78 to 600 µM, with a low detection limit of 1.08 μM (S/N = 3). When the pH varies in the range of 5.5 to 7.5, the sensor maintains a certain level of stability for glucose detection. The presence of lactic acid, urea, and ascorbic acid had minimal impact on glucose detection by the sensor. After 20 days of storage at room temperature, the sensor maintains 80 % efficiency. This study supports the development of wearable glucose sensors with high sensitivity, specificity, and stability through molecular imprinting.

An integrated plant glucose monitoring system based on microneedle-enabled electrochemical sensor

Real-time monitoring of glucose concentration changes in plants and access to plant physiological information timely are of great significance to the development of precision agriculture. Here, we innovatively present an electrochemical sensing device that combines microneedle sensors and 3D printing technology to achieve real-time monitoring of glucose in plants in a minimally invasive manner. The device consists of two components: the inner part features a highly efficient sensing interface based on platinum wire (MPt-Au-Nafion-GOx-Pu), while the outer part consists of polymer microneedles formed by 3D printing. Additionally, the polymer hollow microneedle features a slender tip diameter of only 300 μm, minimizing plant damage during the detection procedure. The device shows good detection performance, with a limit of detection (LOD) of 33.3 μM and a detection sensitivity of 17 nA/μM·cm2. It can detect glucose concentrations in the range of 100 μM to 100 mM, providing a unique solution for timely agronomic management of crops tool. By performing 12 h real-time monitoring and salt stress treat on tomato and aloe vera, the results verified the feasibility of integrated device applied to real-time glucose detection in plants.

A dense SERS substrate of the AgNPs@GO compound film for detecting homocysteine molecules

This study focuses on the development of a highly sensitive surface-enhanced Raman scattering (SERS) sensor for detecting homocysteine (Hcy) molecules. The Hcy sensor was created by depositing silver nanoparticles (AgNPs) onto the surface of graphene oxide (GO) film to form a dense AgNPs@GO composite film. The AgNPs on the composite film interacted with sulfur atoms (S) of Hcy molecules to form Ag-S bonds, which boosted the chemisorption of Hcy molecules and enabled them to be specifically recognized. The SERS sensor exhibited a maximum enhancement factor of up to 1.1 × 104, with a reliable linear response range from 1 to 60 ng mL-1. The limit of detection (LOD) for Hcy molecules was as low as 1.1 × 10-9 M. Moreover, Hcy molecules were successfully distinguished in a mixed solution of γ-aminobutyric acid and Hcy molecules. In this study, a simple preparation process of SERS substrate and a novel detection method for Hcy molecules provided a new pathway for the rapid and effective detection of Hcy molecules in the food and biomedicine fields.

Biosensors with Boronic Acid-Based Materials as the Recognition Elements and Signal Labels

It is of great importance to have sensitive and accurate detection of cis-diol-containing biologically related substances because of their important functions in the research fields of metabolomics, glycomics, and proteomics. Boronic acids can specifically and reversibly interact with 1,2- or 1,3-diols to form five or six cyclic esters. Based on this unique property, boronic acid-based materials have been used as synthetic receptors for the specific recognition and detection of cis-diol-containing species. This review critically summarizes the recent advances with boronic acid-based materials as recognition elements and signal labels for the detection of cis-diol-containing biological species, including ribonucleic acids, glycans, glycoproteins, bacteria, exosomes, and tumor cells. We also address the challenges and future perspectives for developing versatile boronic acid-based materials with various promising applications.

Molecularly Imprinted Nanomaterials with Stimuli Responsiveness for Applications in Biomedicine

The review aims to summarize recent reports of stimuli-responsive nanomaterials based on molecularly imprinted polymers (MIPs) and discuss their applications in biomedicine. In the past few decades, MIPs have been proven to show widespread applications as new molecular recognition materials. The development of stimuli-responsive nanomaterials has successfully endowed MIPs with not only affinity properties comparable to those of natural antibodies but also the ability to respond to external stimuli (stimuli-responsive MIPs). In this review, we will discuss the synthesis of MIPs, the classification of stimuli-responsive MIP nanomaterials (MIP-NMs), their dynamic mechanisms, and their applications in biomedicine, including bioanalysis and diagnosis, biological imaging, drug delivery, disease intervention, and others. This review mainly focuses on studies of smart MIP-NMs with biomedical perspectives after 2015. We believe that this review will be helpful for the further exploration of stimuli-responsive MIP-NMs and contribute to expanding their practical applications especially in biomedicine in the near future.

Arsenic Prodrug-Mediated Tumor Microenvironment Modulation Platform for Synergetic Glioblastoma Therapy

Glioblastoma (GBM) has a distinct internal environment characterized by high levels of glutathione (GSH) and low oxygen partial pressure, which significantly restrict most drugs' effectiveness. Arsenic-based drugs are emerging candidates for treating solid tumors; however, relatively high doses in solo systems and inconsistent complementary systems severely damage the normal tissues. We proposed a novel covalently conjugated strategy for arsenic-based therapy via arsenic-boronic acid complex formation. The boronic acid was modified on silver (AgL) to capture As^V under an alkaline condition named arsenate plasmonic complex (APC) with a distinct Raman response. The APC can precisely release the captured As^V in lysosomal acidic pH that specifically targets TME to initiate a multimodal therapeutic effect such as GSH depletion and reactive oxygen species generation. In addition, GSH activation leads to subconverted As^V into As^III, which further facilitated glutathione peroxidase (GPx) and superoxide dismutase inhibition, whereas the tumor selective etching of the silver core triggered by endogenous H₂O₂ that can oxidize to generate highly toxic Ag ions produces and supplies O₂ to help the alleviated hypoxia. Both in vitro and in vivo data verify the APC-based chemotherapy paving the way for efficient nanomedicine-enabled boronate affinity-based arsenic chemotherapeutics for on demand site-specific cancer combination treatment of GBM tumors.

Colorimetric detection of citric acid as the biomarker for urolithiasis based on sodium dodecylsulfate-AgNPs with a portable CD-spectrometer

Citric acid (CA) has been considered as a biomarker of urolithiasis due to its vital suppression role in urinary stone formation. Most analytical methods for detecting CA are complicated and require expensive equipment. Herein, a colorimetric method based on sodium dodecylsulfate (SDS) modified AgNPs was presented for convenient and portable detection of CA in urine. By detecting the absorption of the solution color, the quantitative detection of CA can be achieved. The pH value of SDS-AgNPs, concentration of Al³⁺ and incubation time were optimized. Under optimal conditions, the method has the detection range of 1-10 mg/L, with a limit of detection (LOD) of 0.21 mg/L. Moreover, a self-developed portable CD(Compact Disk)-spectrometer (CDs) was established for detecting CA with a LOD of 0.49 mg/L featuring high simplicity, low time cost and good portability. This method was also validated with good selectivity to CA. In addition, the artificial urine samples were also detected to verify the capability of the method and CDs. The results validated that the method integrating with the CDs can be a promising platform for citric acid detection that can be further used for early screening and prognostic monitoring of urolithiasis.

Probing low-copy-number proteins in single living cells using single-cell plasmonic immunosandwich assays

Cellular heterogeneity is pervasive and of paramount importance in biology. Single-cell analysis techniques are indispensable for understanding the heterogeneity and functions of cells. Low-copy-number proteins (fewer than 1,000 molecules per cell) perform multiple crucial functions such as gene expression, cellular metabolism and cell signaling. The expression level of low-copy-number proteins of individual cells provides key information for the in-depth understanding of biological processes and diseases. However, the quantitative analysis of low-copy-number proteins in a single cell still remains challenging. To overcome this, we developed an approach called single-cell plasmonic immunosandwich assay (scPISA) for the quantitative measurement of low-copy-number proteins in single living cells. scPISA combines in vivo microextraction for specific enrichment of target proteins from cells and a state-of-the-art technique called plasmon-enhanced Raman scattering for ultrasensitive detection of low-copy-number proteins. Plasmon-enhanced Raman scattering detection relies on the plasmonic coupling effect (hot-spot) between silver-based plasmonic nanotags and a gold-based extraction microprobe, which dramatically enhances the signal intensity of the surface-enhanced Raman scattering of the nanotags and thereby enables sensitivity at the single-molecule level. scPISA is a straightforward and minimally invasive technique, taking only ~6-15 min (from in vivo extraction to Raman spectrum readout). It is generally applicable to all freely floating intracellular proteins provided that appropriate antibodies or alternatives (for example, molecularly imprinted polymers or aptamers) are available. The entire protocol takes ~4-7 d to complete, including material fabrication, single-cell manipulation, protein labeling, signal acquisition and data analysis.

Molecularly Imprinted Polymer (MIP) Applications in Natural Product Studies Based on Medicinal Plant and Secondary Metabolite Analysis

Characterization and extraction of plant secondary metabolites are important in agriculture, pharmaceutical, and food industry. In this regard, the applied analytical methods are mostly costly and time-consuming; therefore, choosing a suitable approach is essential for optimum results and economic suitability. One of the recently considered methods used to characterize new types of materials is MIPs. Among the various applications of MIPs is the identification and separation of various plant-derived compounds, such as secondary metabolites, chemical residues, and pesticides. The present review describes the application of MIPs as a tool in medicinal plant material analysis, focusing on plant secondary metabolism.

Molecular-Imprinting-Based Surface-Enhanced Raman Scattering Sensors

Molecularly imprinted polymers (MIPs) receive extensive interest, owing to their structure predictability, recognition specificity, and application universality as well as robustness, simplicity, and inexpensiveness. Surface-enhanced Raman scattering (SERS) is regarded as an ideal optical detection candidate for its unique features of fingerprint recognition, nondestructive property, high sensitivity, and rapidity. Accordingly, MIP based SERS (MIP-SERS) sensors have attracted significant research interest for versatile applications especially in the field of chemo- and bioanalysis, showing excellent identification and detection performances. Herein, we comprehensively review the recent advances in MIP-SERS sensors construction and applications, including sensing principles and signal enhancement mechanisms, focusing on novel construction strategies and representative applications. First, the basic structure of the MIP-SERS sensors is briefly outlined. Second, novel imprinting strategies are highlighted, mainly including multifunctional monomer imprinting, dummy template imprinting, living/controlled radical polymerization, and stimuli-responsive imprinting. Third, typical application of MIP-SERS sensors in chemo/bioanalysis is summarized from both small and macromolecular aspects. Lastly, the challenges and perspectives of the MIP-SERS sensors are proposed, orienting sensitivity improvement and application expanding.

From single cells to complex tissues in applications of surface-enhanced Raman scattering

This tutorial review explores how three of the most common methods for introducing nanoparticles to single cells for surface-enhanced Raman scattering measurements can be adapted for experiments with complex tissues.

Molecularly Imprinted Polymer-Based Hybrid Materials for the Development of Optical Sensors

We report on the development of new optical sensors using molecularly imprinted polymers (MIPs) combined with different materials and explore the novel strategies followed in order to overcome some of the limitations found during the last decade in terms of performance. This review pretends to offer a general overview, mainly focused on the last 3 years, on how the new fabrication procedures enable the synthesis of hybrid materials enhancing not only the recognition ability of the polymer but the optical signal. Introduction describes MIPs as biomimetic recognition elements, their properties and applications, emphasizing on each step of the fabrication/recognition procedure. The state of the art is presented and the change in the publication trend between electrochemical and optical sensor devices is thoroughly discussed according to the new fabrication and micro/nano-structuring techniques paving the way for a new generation of MIP-based optical sensors. We want to offer the reader a different perspective based on the materials science in contrast to other overviews. Different substrates for anchoring MIPs are considered and distributed in different sections according to the dimensionality and the nature of the composite, highlighting the synergetic effect obtained as a result of merging both materials to achieve the final goal.

Rapid microwave-assisted distillation–precipitation polymerization for the synthesis of magnetic molecular imprinted polymers coupled to HPTLC determination of perphenazine in human urine

Microwave-assisted distillation–precipitation polymerization (MWDPP) for the synthesis of magnetic molecularly imprinted polymers (MMIPs) under atmospheric pressure is reported.