Biosensing Technologies for Mycobacterium tuberculosis Detection: Status and New Developments

Biosensing technologies promise to improve Mycobacterium tuberculosis (M. tuberculosis) detection and management in clinical diagnosis, food analysis, bioprocess, and environmental monitoring. A variety of portable, rapid, and sensitive biosensors with immediate “on-the-spot” interpretation have been developed for M. tuberculosis detection based on different biological elements recognition systems and basic signal transducer principles. Here, we present a synopsis of current developments of biosensing technologies for M. tuberculosis detection, which are classified on the basis of basic signal transducer principles, including piezoelectric quartz crystal biosensors, electrochemical biosensors, and magnetoelastic biosensors. Special attention is paid to the methods for improving the framework and analytical parameters of the biosensors, including sensitivity and analysis time as well as automation of analysis procedures. Challenges and perspectives of biosensing technologies development for M. tuberculosis detection are also discussed in the final part of this paper

A Light-Responsive Reversible Molecule-Gated System Using Thymine-Modified Mesoporous Silica Nanoparticles

In this paper, a reversible light-responsive molecule-gated system based on mesoporous silica nanoparticles (MSN) functionalized with thymine derivatives is designed and demonstrated. The closing/opening protocol and release of the entrapped guest molecules is related by a photodimerization–cleavage cycle of thymine upon different irradiation. In the system, thymine derivatives with hydrophilicity and biocompatibility were grafted on the pore outlets of MSN. The irradiation with 365 nm wavelength UV light to thymine-functionalized MSN led to the formation of cyclobutane dimer in the pore outlet, subsequently resulting in blockage of pores and strongly inhibiting the diffusion of guest molecules from pores. With 240 nm wavelength UV light irradiation, the photocleavage of cyclobutane dimer opened the pore and allowed the release of the entrapped guest molecules. As a proof-of-the-concept, Ru­(bipy)₃²⁺ was selected as the guest molecule. Then the light-responsive loading and release of Ru­(bipy)₃²⁺ were investigated. The results indicated that the system had an excellent loading amount (53 μmol g^–1 MSN) and controlled release behavior (82% release after irradiation for 24 h), and the light-responsive loading and release procedure exhibited a good reversibility. Besides, the light-responsive system loaded with Ru­(bipy)₃²⁺ molecule could also be used as a light-switchable oxygen sensor

Regenerable Multifunctional Mesoporous Silica Nanocomposites for Simultaneous Detection and Removal of Mercury(II)

Mercury (Hg²⁺) is a highly toxic and widespread environmental pollutant. Herein, a regenerable and highly selective core–shell structured magnetic mesoporous silica nanocomposite with functionalization of thymine (T) and T-rich DNA (denoted as Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposite) has been developed for simultaneous detection and removal of Hg²⁺. In this work, the thymine and T-rich DNA were immobilized onto the interior and exterior surface of outermost mesoporous silica, respectively. The detection mechanism is based on Hg²⁺-mediated hairpin structure formed by T-rich DNA functionalized on the exterior surface of the nanocomposites, where, upon addition of SYBR Green I dye, strong fluorescence is observed. In the absence of Hg²⁺, however, addition of the dye results in low fluorescence. The limit of detection for Hg²⁺ in a buffer is 2 nM by fluorescence spectroscopy. Simultaneously, the Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposite features a selective binding with Hg²⁺ between two thymines immobilized at the interior surface of the mesopores and exhibits efficient and convenient Hg²⁺ removal by a magnet. Kinetic study reveals that the Hg²⁺ removal is a rapid process with over 80% of Hg²⁺ removed within approximately 1 h. The applicability of the developed nanocomposites is demonstrated to detect and remove Hg²⁺ from samples of Xiangjiang river water spiked with Hg²⁺. In addition, distinguishing aspects of the Fe₃O₄@nSiO₂@mSiO₂-T-TRDNA nanocomposites for Hg²⁺ detection and removal also include the regeneration using a simple acid treatment and resistance to nuclease digestion. Similar process can be used to functionalize the Fe₃O₄@nSiO₂@mSiO₂ nanocomposites with other nucleic acids and small molecules for environmental and biomedical applications

Label-Free Homogeneous Electrochemical Sensing Platform for Protein Kinase Assay Based on Carboxypeptidase Y‑Assisted Peptide Cleavage and Vertically Ordered Mesoporous Silica Films

Presented herein is a simple, robust, and label-free homogeneous electrochemical sensing platform constructed for the detection of protein kinase activity and inhibition by integration of carboxypeptidase Y (CPY)-assisted peptide cleavage reaction and vertically ordered mesoporous silica films (MSFs). In this sensing platform, the substrate peptide composed of kinase-specific recognized sequence and multiple positively charged arginine (R) residues was ingeniously designed. In the presence of protein kinase, the substrate peptide was phosphorylated and then immediately resisted CPY cleavage. The phosphorylated peptide could be effectively adsorbed on the negatively charged surface of MSFs modified indium–tin oxide (ITO) electrode (MSFs/ITO) by noncovalent electrostatic attraction. The adsorbed peptide was subsequently used as a hamper to prevent the diffusion of electroactive probe (FcMeOH) to the electrode surface through the vertically aligned nanopores, resulting in a detectable reduction of electrochemical signal. As demonstrated for the feasibility and universality of the sensing platform, both protein kinase A (PKA) and casein kinase II (CK2) were selected as the models, and the detection limits were determined to be 0.083 and 0.095 UmL^–1, respectively. This sensing platform had the merits of simplicity, easy manipulation, and improved phosphorylation and cleavage efficiency, which benefited from homogeneous solution reactions without sophisticated modification or immobilization procedures. In addition, given the key role of inhibition and protein kinase activity detection in cell lysates, this proposed sensing platform showed great potential in kinase-related bioanalysis and clinical biomedicine

Poly(thymine)-Templated Copper Nanoparticles as a Fluorescent Indicator for Hydrogen Peroxide and Oxidase-Based Biosensing

Biomineralized fluorescent metal nanoparticles have attracted considerable interest in many fields by virtue of their excellent properties in synthesis and application. Poly­(thymine)-templated fluorescent copper nanoparticles (T-CuNPs) as a promising nanomaterial has been exploited by us recently and displays great potential for signal transducing in biochemical analysis. However, the application of T-CuNPs is rare and still at an early stage. Here, a new fluorescent analytical strategy has been developed for H₂O₂ and oxidase-based biosensing by exploiting T-CuNPs as an effective signal indicator. The mechanism is mainly based on the poly­(thymine) length-dependent formation of T-CuNPs and the probe’s oxidative cleavage. In this assay, the probe T40 can effectively template the formation of T-CuNPs by a fast <i>in situ</i> manner in the absence of H₂O₂, with high fluorescent signal, while the probe is cleaved into short-oligonucleotide fragments by hydroxyl radical (·OH) which is formed from the Fenton reaction in the presence of H₂O₂, leading to the decline of fluorescence intensity. By taking advantage of H₂O₂ as a mediator, this strategy is further exploited for oxidase-based biosensing. As the proof-of-concept, glucose in human serum has been chosen as the model system and has been detected, and its practical applicability has been investigated by assay of real clinical blood samples. Results demonstrate that the proposed strategy has not only good detection capability but also eminent detection performance, such as simplicity and low-cost, holding great potential for constructing effective sensors for biochemical and clinical applications

DNA-Functionalized Hollow Mesoporous Silica Nanoparticles with Dual Cargo Loading for Near-Infrared-Responsive Synergistic Chemo-Photothermal Treatment of Cancer Cells

Low drug loading, premature drug leakage, and intratumoral genetic heterogeneity are three main challenges that hinder the successful nanotherapeutics-based oncotherapy, as they provide insufficient therapeutic efficacy, systematic adverse effects, and multidrug resistance, respectively. To address these challenges, we herein develop near-infrared (NIR) laser-sensitive DNA-modified hollow mesoporous silica nanoparticles (HMSNs) with dual cargo loading for chemo-photothermal combined treatment of tumors. Starting from the zeolitic imidazolate framework-8 (ZIF-8) template, a layer of mesoporous silica is coated on ZIF-8 (ZIF-8@MSNs), and subsequently the template is self-degraded under acidic conditions to obtain HMSNs. It is demonstrated that the as-made HMSNs possesses a well-defined morphology, large hollow cavities, and abundant mesoporous structures. After loading of indocyanine green into HMSNs’ core (ICG@HMSNs), the DNA strands, which are composed by sequential cytosine-guanine (CG) base pairs, are then grafted onto the ICG@HMSNs (DNA-ICG@HMSNs) to provide loading sites for anticancer drug doxorubicin (DOX). The as-prepared DOX-inserted DNA-ICG@HMSNs (DOX@DNA-ICG@HMSNs) shows highly efficient transformation of light energy into thermal energy. Additionally, the loading amount of ICG is determined to be 930 mg g^–1 SiO₂, which is more than 30 times compared to that in MCM-41-type MSNs. <i>In vitro</i> experiments using HeLa cells demonstrate that this NIR-laser-responsive drug delivery system (DDSs) enables triggerable cargo release, presumably by heat-induced disruption of the modified DNA double strands. Most importantly, <i>in vitro</i> evaluation and preliminary <i>in vivo</i> investigations independently verified that the combination of triggered chemotherapy and NIR-laser-based hyperthermal therapy results in a better therapeutic effect than individual monotherapies. With these superior properties, we expect that these multifunctional DDSs would promote the application of HMSNs in nanomedical applications

Highly Fe³⁺-Selective Fluorescent Nanoprobe Based on Ultrabright N/P Codoped Carbon Dots and Its Application in Biological Samples

Measuring the levels of Fe³⁺ in human body has attracted considerable attention for health monitoring as it plays an essential role in many physiological processes. In this work, we reported a selective fluorescent nanoprobe for Fe³⁺ detection in biological samples based on ultrabright N/P codoped carbon dots. By employing adenosine 5′-triphosphate (ATP) as the carbon, nitrogen, and phosphorus source, the N/P codoped carbon dots could be simply prepared through hydrothermal treatment. The obtained carbon dots exhibited high quantum yields up to 43.2%, as well as excellent photostability, low toxicity, and water solubility. Because of the Fe–O–P bonds formed between Fe³⁺ and the N/P codoped carbon dots, this nanoprobe showed high selectivity toward Fe³⁺ against various potential interfering substances in the presence of EDTA. The fluorescence quenching of as-fabricated carbon dots was observed with the increasing Fe³⁺ concentration, and the calibration curve displayed a wide linear region over the range of 1–150 μM with a detection limit of 0.33 μM. The satisfactory accuracy was further confirmed with the river samples and ferrous sulfate tablets, respectively. With the above outstanding properties, these N/P codoped carbon dots were successfully applied for direct detection of Fe³⁺ in biological samples including human blood serum and living cells. As compared to the most reported carbon dots-based Fe³⁺ sensors, this nanoprobe showed high fluorescence, good accuracy, and excellent selectivity, which presents the potential practical application for diagnosis of Fe³⁺ related disease

Synthesis of Hollow Mesoporous Silica Nanorods with Controllable Aspect Ratios for Intracellular Triggered Drug Release in Cancer Cells

Here, we have reported a straightforward and effective synthetic strategy for synthesis of aspect-ratios-controllable mesoporous silica nanorods with hollow structure (hMSR) and its application for transcription factor (TF)-responsive drug delivery intracellular. Templating by an acid-degradable nickel hydrazine nanorods (NHNT), we have first synthesized the hollow dense silica nanorods and then coated on a mesoporous silica layer. Subsequently, the dense silica layer was removed by the surface-protected etching method and the hollow structure of hMSR was finally formed. The aspect ratios of the hMSR can be conveniently controlled by regulating the aspect ratios of NHNT. Four different hMSR with aspect ratios of ca. 2.5, ca. 5.3, ca. 8.1, and ca. 9.0 has been obtained. It was demonstrated that the as-prepared hMSRs have good stability, high drug loading capacity, and fast cell uptake capability, which makes them to a potential nanocarrier for drug delivery. As the paradigm, hMSR with an aspect ratio of ca. 8.1 was then applied for TF-responsive intracellular anticancer drug controlled release by using a Ag⁺-stabilized molecular switch of triplex DNA (TDNA) as capping agents and probes for TFs recognition. In the presence of TF, the pores of hMSR can be unlocked by the TFs induced disassembly of TDNA, leading to the leakage of DOX. The research in vitro displayed that this system has a TFs-triggered DOX release, and the cytotoxicity in L02 normal cells was lower than that of HeLa cells. We hope that this developed hMSR-based system will promote the development of cancer therapy in related fields