Motion-driven sensing and biosensing using electrochemically propelled nanomotors

Electrochemically-propelled nanomotors offer considerable promise for developing new and novel bioanalytical and biosensing strategies based on the direct isolation of target biomolecules or changes in their movement in the presence of target analytes. For example, receptor-functionalized nanomotors offer direct and rapid target isolation from raw biological samples without preparatory and washing steps. Microtube engines functionalized with ss-DNA, aptamer or antibody receptors are particularly useful for the direct isolation of nucleic acids, proteins or cancer cells, respectively. A new nanomotor-based signal transduction involving measurement of speed and distance travelled by nanomotors, offers highly sensitive, rapid, simple and low cost detection of target biomarkers, and a new dimension of analytical information based on motion. The resulting distance signals can be easily visualized by optical microscope (without any sophisticated analytical instrument) to reveal the target presence and concentration. The attractive features of the new micromachine-based target isolation and signal transduction protocols reviewed in this article offer numerous potential applications in biomedical diagnostics, environmental monitoring, and forensic analysis.     

Synthesis of aptamer-functionalized Ag nanoclusters for MCF-7 breast cancer cells imaging

Aptamer-functionalized silver nanoclusters(Ag NCs) have been attracting a lot of interest as label-free probes which have been successfully applied to both cell imaging and molecular detection.MUCl aptamer is an ssDNA aptamer that specifically binds to MUCl mucin which is a large transmembrane glycoprotein whose expression level increases at least 10-fold in primary and metastatic breast cancers.Using C4A4C3-linker-MUCl as template,the Ag NCs were synthesized through one-pot process.The fluorescence intensity of Ag NCs was found to be closely related to the length and type(poly adenine or thymine) of the linker,the optimum linker being-AAAAA-.Using the C4A4C3-A5-MUC1 as the scaffold,the synthesized Ag NCs emitted fluorescence with high quantum yield(QY) of 66.5%.Based on the specific interaction between the MUCl aptamer and MUCl mucin,the C4A4C3-A5-MUC1-stabilized Ag NCs could recognize and differentiate the MCF-7 breast cancer cells from MDA-MB-231 breast cancer and A549 human lung cancer cells.     

Aptamer‐based thrombin assay on microfluidic platform

A facile and sensitive aptamer‐based protocol has been developed for protein assay on microfluidic platform with fluorescence detection using an off‐chip microarray scanner. Aptamer‐functionalized magnetic beads were used to capture thrombin that binds to a second aptamer fluorescently labeled by Cy3. Experimental conditions, such as incubation time and temperature, washing time, interfering proteins, and aptamer, etc., were optimized for the microchip method. This work demonstrated there was a good relationship between fluorescence intensity and thrombin concentration in the range of 65–1000 ng/mL with the RSD less than 8%. Notably, an analysis only needs 1 μL volume of sample injection and this system can capture extremely tiny amount thrombin (0.4 fmol). This method has been successfully applied to assay of thrombin in human serum with the recovery of 79.74–95.94%.     

Near‐Infrared‐Light‐Mediated Imaging of Latent Fingerprints based on Molecular Recognition

Photoluminescence is one of the most sensitive techniques for fingerprint detection, but it also suffers from background fluorescence and selectivity at the expense of generality. The method described herein integrates the advantages of near‐infrared‐light‐mediated imaging and molecular recognition. In principle, upconversion nanoparticles (UCNPs) functionalized with a lysozyme‐binding aptamer were used to detect fingerprints through recognizing lysozyme in the fingerprint ridges. UCNPs possess the ability to suppress background fluorescence and make it possible for fingerprint imaging on problematic surfaces. Lysozyme, a universal compound in fingerprints, was chosen as the target, thus simultaneously meeting the selectivity and generality criteria in photoluminescence approaches. Fingerprints on different surfaces and from different people were detected successfully. This strategy was used to detect fingerprints with cocaine powder by using UCNPs functionalized with a cocaine‐binding aptamer.     

Label-Free and Simple G-quadruplex-based Turn-Off Fluorescence Assay for the Detection of Kanamycin

We have developed a label-free and turn-off fluorescence assay for the determination of kanamycin. The detection system consists of an aptamer for specifically recognizing kanamycin and two auxiliary probes functionalized with two GGG repeats at the 3′ or 5′ ends for signal reporting. Two probes both hybridize with the aptamer and then their G-rich sequences combine to form a G-quadruplex. When thioflavin T, a fluorophore, is bound to the G-quadruplex, the fluorescence intensity of the solution dramatically increases. Upon the addition of the kanamycin, the aptamer–kanamycin binding inhibits the hybridization of two probes and aptamer, and restrains the GGG repeats from getting closer to form the G-quadruplex structure, resulting a significant decrease in the fluorescence intensity. The proposed aptamer-based fluorescent sensing platform showed a linear relationship with the concentration of kanamycin from 0.6 to 20.0?nM. The detection limit was determined to be 0.33?nM. The sensing platform provides resistance to interferences from other antibiotics and can be used to efficiently recognize kanamycin in real samples.     

Nanomotors Sense Local Physicochemical Heterogeneities in Tumor Microenvironments**

The invasion of cancer is brought about by continuous interaction of malignant cells with their surrounding tissue microenvironment. Investigating the remodeling of local extracellular matrix (ECM) by invading cells can thus provide fundamental insights into the dynamics of cancer progression. In this paper, we use an active untethered nanomechanical tool, realized as magnetically driven nanomotors, to locally probe a 3D tissue culture environment. We observed that nanomotors preferentially adhere to the cancer-proximal ECM and magnitude of the adhesive force increased with cell lines of higher metastatic ability. We experimentally confirmed that sialic acid linkage specific to cancer-secreted ECM makes it differently charged, which causes this adhesion. In an assay consisting of both cancerous and non-cancerous epithelia, that mimics the in vivo histopathological milieu of a malignant breast tumor, we find that nanomotors preferentially decorate the region around the cancer cells.     

核酸适体功能化的二维材料场效应晶体管传感器研究进展

二维材料场效应晶体管传感器具有可调的电学性质和高的灵敏度, 非常适合用于构建高性能的传感器, 应用于疾病诊断和环境监测等领域. 核酸适体是一种生物识别分子, 具有特异性强、 稳定性高等优势. 近年来, 核酸适体功能化的二维材料场效应晶体管传感器在医疗诊断和环境监测等领域取得了显著的研究进展. 本文综合评述了核酸适体功能化的二维材料场效应晶体管传感器的最新研究进展, 对场效应晶体管传感器的结构及传感原理进行了概括, 详细介绍了二维材料的制备方法以及核酸适体功能化器件的设计原理. 在此基础上, 对核酸适体功能化的二维材料场效应晶体管传感器在疾病诊断和环境监测领域的应用进展进行了概述, 讨论了核酸适体功能化的二维材料场效应晶体管传感器面临的一些问题和挑战, 对其发展前景进行了展望.     

A novel sensing platform using aptamer and RNA polymerase-based amplification for detection of cancer cells

Cancer is one of the most serious and lethal diseases around the world. Its early detection has become a challenging goal. To address this challenge, we developed a novel sensing platform using aptamer and RNA polymerase-based amplification for the detection of cancer cells. The assay uses the aptamer as a capture probe to recognize and bind the tumor marker on the surface of the cancer cells, forming an aptamer-based sandwich structure for collection of the cells in the microplate wells, and uses SYBR Green II dye as a tracer to produce strong fluorescence signal. The tumor marker interacts first with the recognition probes which were composed of the aptamer and single-stranded T7 RNA polymerase promoter. Then, the recognition probe hybridized with template probes to form a double-stranded T7 RNA polymerase promoter. This dsDNA region is extensively transcribed by T7 RNA polymerase to produce large amounts of RNAs, which are easily monitored using the SYBR Green II dye and a standard fluorometer, resulting in the amplification of the fluorescence signal. Using MCF-7 breast cancer cell as the model cell, the present sensing platform showed a linear range from 5.0 × 10² to 5.0 × 10⁶ cells mL⁻¹ with a detection limit of 5.0 × 10² cells mL⁻¹. This work suggested a strategy to use RNA signal amplification combining aptamer recognition to develop a highly sensitive and selective method for cancer cells detection.     

核酸适配体功能化的稀土上转换纳米材料在生物检测中的应用

稀土上转换纳米材料可以吸收近红外光并发射出可见光或紫外光,在生物传感领域得到了广泛研究。核酸适配体能高特异性和高亲和性地与靶标物结合,被广泛应用于生物传感、疾病诊断等领域。将稀土上转换纳米材料与核酸适配体结合构建的检测体系,可实现对目标物灵敏、高选择性的检测。本文介绍了近几年核酸适配体功能化的稀土上转换纳米材料在生物小分子、蛋白质、核酸、病原微生物、细胞等方面的应用,并展望了其在分析检测领域的发展前景。     

High-intensity fluorescence imaging and sensitive electrochemical detection of cancer cells by using an extracellular supramolecular reticular DNA-quantum dot sheath

Acting as a cage-type cellular probe, an extracellular supramolecular reticular DNA-quantum dot (QD) sheath has been developed for high-intensity fluorescence microscopy imaging and the sensitive electrochemical detection of Ramos cells. The extracellular supramolecular reticular DNA-QD sheath is constructed from layer-by-layer self-assembly of DNA-CdTe QD probes and DNA nanowire frameworks functionalized with a Ramos cell-binding aptamer. The DNA-QD sheath forms specifically and quickly on the surface of Ramos cells at physiological temperature, and the assembly of large numbers of DNA-CdTe QD probes on the surface of Ramos cells produces exceedingly high fluorescence intensity. Using the extracellular supramolecular reticular DNA-QD sheath as the cellular probe, Ramos cells can be clearly observed and easily distinguished from a mixture of multiple cancer cells by fluorescence microscopy imaging. Using the new cage-type cellular probe, a sensitive sandwich-type electrochemical strategy has also been developed to achieve accurate quantitative analysis of Ramos cells. Under the optimized conditions, Ramos cells can be detected quantitatively in a range from 10 to 1000 cells with a detection limit of 10 cells. This strategy presents a promising platform for highly sensitive and convenient evaluation of cancer cell levels.     

Sensitive detection of human breast cancer cells based on aptamer–cell–aptamer sandwich architecture

Breast cancer is one of the most critical threats to the health of women, and the development of new methods for early diagnosis is urgently required, so this paper reports a method to detect Michigan cancer foundation-7 (MCF-7) human breast cancer cells with considerable sensitivity and selectivity by using electrochemical technique. In this method, a mucin 1 (MUC1)-binding aptamer is adopted to recognize MCF-7 human breast cancer cells, while enzyme labeling is employed to produce amplified catalytic signals. The molecular recognition and the signal amplification are elaborately integrated by fabricating an aptamer–cell–aptamer sandwich architecture on an electrode surface, thus a biosensor for the detection of MCF-7 is fabricated based on the architecture. The detection range can be from 100 to 1 × 10⁷ cells, and the detection limit can be as low as 100 cells. The method is also cost-effective and conveniently operated, implying potential help for the development of early diagnosis of breast cancer.     

FRET-based aptamer probe for rapid angiogenin detection

A sensitive method for rapid angiogenin (Ang) detection based on fluorescence resonance energy transfer (FRET) has been described. A dual-labeled probe based on high affinity aptamer for Ang was constructed. As donor and acceptor, 6-carboxyfluorescein (FAM) and 6-carboxy-tetramethylrhodamine (TMR) were labeled at 5'- and 3'-termini of the aptamer probe, respectively. The dual-labeled probe showed obvious fluorescence changes due to the specific binding between aptamer and Ang. By monitoring the fluorescence intensity of donor and acceptor, quantitative Ang detection could be achieved. This assay is highly specific and sensitive, with a detection limit of 2.0 x 10(-10) mol L(-1) and a linear range of 5.0 x 10(-10) to 4.0 x 10(-8) mol L(-1) Ang. Ang in serum samples of health and lung cancer were also detected.     

Degradable intracellular self-functionalized nanoprobes for in vitro diagnosis and monitoring of cancer

Despite various attempts to accelerate nanoparticle clearance from the cell, considerable amounts of nanomaterials remain in the cell, impairing cellular activities and hence precluding reliable invitro diagnosis. Retention of nanoparticles in cellular organelles disturbs cellular equilibrium and induces long-term consequences such as change in cell phenotype, genotype, cell mobility, toxicity, and even cell death. As a result, it is necessary to produce nanoparticles that degrade promptly and are then safely expelled from the cell while remaining biocompatible and fully functional. Here, we present a metabolizable organic carbon probe functionalized for Raman and fluorescence that can be used to track and monitor metabolizable organic carbon probe breakdown in lysosomes while simultaneously performing molecular level probing for invitro cancer diagnosis. The probes were stable in medium and other fluids and degraded in cancer cells within a week. The probes demonstrated an excellent Raman signal, which allowed surface-enhanced Raman spectroscopy-based monitoring of the degradation. Additionally, the probes showed the property of fluorescence which can be attributed to the inherent fluorescence of the probe on quantum scale. Experimental evidence of self-metabolization of the probe was further demonstrated. We tested the ability of the probes for cancer diagnosis with two cancer cell lines (breast and lung) and experimentally demonstrated the ability to discriminate between breast cancer and lung cancer without any ambiguity. These findings establish a novel type of functionalized degradable nanostructure for intracellular sensing and imaging cancer cells in cellular nanomedicine.     

Adenosine triphosphate detection by controlled-release of carboxy fluorescein from mesoporous silica nanoparticles blocked with aptamer-based gold nanoparticles

In this paper, an adenosine-5′-triphosphate (ATP) controlled-release strategy to construct a fluorescence sensing platform has been designed. In the sensing platform, because of ATP aptamer and singlestranded DNA (ssDNA)-linked mesoporous silica nanoparticles (Si-MPs) were hybridized, the pores of Si-MPs were blocked with Au nanoparticles (AuNPs) modified with ATP aptamer. Carboxy fluorescein was plugged in channels of Si-MPs. In the presence of target molecule ATP, the ATP aptamer combined with ATP and the AuNPs got away from the pore of the surface of Si-MPs modified by ssDNA. 5-Carboxyfluorescein molecule was released to allow the fluorescent detection. By monitoring the fluorescence at 518 nm, ATP could be quantitatively detected with a detection limit of 6 × 10^–8 M. The linear response range was 6 × 10^–8 to 1 × 10^–6 M. This assay was also able to discriminate ATP from its analogs. The controlled-release aptamer-based biosensor could have an effective application in human breast cancer MCF-7 cells.     

Bioinspired Engineering of a Multivalent Aptamer‐Functionalized Nanointerface to Enhance the Capture and Release of Circulating Tumor Cells

Circulating tumor cell (CTC)‐enrichment by using aptamers has a number of advantages, but the issue of compromised binding affinities and stabilities in real samples hinders its wide applications. Inspired by the high efficiency of the prey mechanism of the octopus, we engineered a deterministic lateral displacement (DLD)‐patterned microfluidic chip modified with multivalent aptamer‐functionalized nanospheres (AP‐Octopus‐Chip) to enhance capture efficiency. The multivalent aptamer–antigen binding efficiency improves 100‐fold and the capture efficiency is enhanced more than 300 % compared with a monovalent aptamer‐modified chip. Moreover, the captured cancer cells can be released through a thiol exchange reaction with up to 80 % efficiency and 96 % viability, which is fully compatible with downstream mutation detection and CTC culture. Using the chip, we were able to find CTCs in all cancer samples analyzed.     

Aptamer-based analysis of angiogenin by fluorescence anisotropy

Recognition and monitoring proteins in real time and in homogeneous solution has always been a difficult task. Here, we introduce a signal transduction strategy for quick protein recognition and real-time quantitative analysis in homogeneous solutions based on a high-affinity aptamer for protein angiogenin (Ang). The method takes advantage of the sensitive anisotropy signal change of fluorophore-labelled aptamer upon protein/aptamer binding. When the labelled aptamer is bound with its target protein Ang, the increased molecular weight causes the rotational motion of the fluorophore attached to the complex to become much slower. Therefore, increasing the amount of Ang results in a raised anisotropy value of the Ang/aptamer. By monitoring the anisotropy change, we are able to detect the binding events between the aptamer and Ang, and measure Ang concentration quantitatively in homogeneous solutions. This assay is highly selective, with a detection limit of 1 nM of Ang. The dissociation constant of the Ang/aptamer binding is determined in the nanomolar range and changes with increasing salt concentration. One can also use our assay to compare the binding affinities of different ligands for the target molecule. Ang in serum samples of malignant lung cancer was also detected. Efficient protein detection using aptamer-based fluorescence anisotropy measurements is expected to find wide applications in protein monitoring, cancer diagnosis, drug screening and other fields.     

Metal-enhanced fluorescence of nano-core–shell structure used for sensitive detection of prion protein with a dual-aptamer strategy

Metal-enhanced fluorescence (MEF) as a newly recognized technology is widespread throughout biological research. The use of fluorophore–metal interactions is recognized to be able to alleviate some of fluorophore photophysical constraints, favorably increase both the fluorophore emission intensity and photostability. In this contribution, we developed a novel metal-enhanced fluorescence (MEF) and dual-aptamer-based strategy to achieve the prion detection in solution and intracellular protein imaging simultaneously, which shows high promise for nanostructure-based biosensing. In the presence of prion protein, core–shell Ag@SiO₂, which are functionalized covalently by single stranded aptamer (Apt1) of prions and Cyanine 3 (Cy3) decorated the other aptamer (Apt2) were coupled together by the specific interaction between prions and the anti-prion aptamers in solution. By adjusting shell thickness of the pariticles, a dual-aptamer strategy combined MEF can be realized by the excitation and/or emission rates of Cy3. It was found that the enhanced fluorescence intensities followed a linear relationship in the range of 0.05–0.30 nM, which is successfully applied to the detection of PrP in mice brain homogenates.     

A Fluorescent Polymeric Quantum Dot/Aptamer Superstructure and Its Application for Imaging of Cancer Cells

In this work, a novel polymeric quantum dot/aptamer superstructure with a highly intense fluorescence was fabricated by a molecular engineering strategy and successfully applied to fluorescence imaging of cancer cells. The polymeric superstructure, which is composed of both multiple cell‐based aptamers and a high ratio of quantum dot (QD)‐labeled DNA, exploits the target recognition capability of the aptamer, an enhanced cell internalization through multivalent effects, and cellular disruption by the polymeric conjugate. Importantly, the polymeric superstructure exhibits an increasingly enhanced fluorescence with recording time and is thus suitable for long‐term fluorescent cellular imaging. The unique and excellent fluorescence property of the QD superstructure paves the way for developing polymeric QD superstructures that hold promise for applications such as in vivo imaging.     

A sensitive fluorescence anisotropy method for detection of lead (II) ion by a G-quadruplex-inducible DNA aptamer

Sensitive and selective detection of Pb²⁺ is of great importance to both human health and environmental protection. Here we propose a novel fluorescence anisotropy (FA) approach for sensing Pb²⁺ in homogeneous solution by a G-rich thrombin binding aptamer (TBA). The TBA labeled with 6-carboxytetramethylrhodamine (TMR) at the seventh thymine nucleotide was used as a fluorescent probe for signaling Pb²⁺. It was found that the aptamer probe had a high FA in the absence of Pb²⁺. This is because the rotation of TMR is restricted by intramolecular interaction with the adjacent guanine bases, which results in photoinduced electron transfer (PET). When the aptamer probe binds to Pb²⁺ to form G-quadruplex, the intramolecular interaction should be eliminated, resulting in faster rotation of the fluorophore TMR in solution. Therefore, FA of aptamer probe is expected to decrease significantly upon binding to Pb²⁺. Indeed, we observed a decrease in FA of aptamer probe upon Pb²⁺ binding. Circular dichroism, fluorescence spectra, and fluorescence lifetime measurement were used to verify the reliability and reasonability of the sensing mechanism. By monitoring the FA change of the aptamer probe, we were able to real-time detect binding between the TBA probe and Pb²⁺. Moreover, the aptamer probe was exploited as a recognition element for quantification of Pb²⁺ in homogeneous solution. The change in FA showed a linear response to Pb²⁺ from 10 nM to 2.0 μM, with 1.0 nM limit of detection. In addition, this sensing system exhibited good selectivity for Pb²⁺ over other metal ions. The method is simple, quick and inherits the advantages of aptamer and FA.     

Micro/Nanomotors for Water Purification

Self-propelled micro/nanomotors are synthetic machines that can convert different sources of energy into motion; at the same time, they are able to serve innovative environmental applications, for example, water purification. The self-propelled micro and nanomachines can rapidly zoom through the solution, carrying catalytic surface or chemical to remove or degrade pollutants in a much faster fashion than that of static systems, which depend on diffusion and fluxes. This review highlights the recent progress of micro/nanomotors in water pollutant detection and pollutant removal applications.