A Practical Electrochemical Nanotool for Facile Quantification of Amino Acids in Single Cell

Iontronic Photoelectrochemical Biorecognition Probing

Herein, the first iontronic photoelectrochemical (PEC) biorecognition probing is devised by rational engineering of a dual-functional bioconjugate, i.e., a light-sensitive intercalated structural DNA, as a smart gating module confined within a nanotip, which could respond to both the incident light and biotargets of interest. Light stimulation of the bioconjugate could intensify the negative charge at the nano-orifice to sustain enhanced ionic current. The presence of proteins (e.g., acetylcholinesterase, AChE) or nucleic acids (e.g., microRNA (miR)-10b) could lead to bioconjugate release with altered ionic signaling. The practical applicability of the methodology is confirmed by AChE detection in human serum and miR-10b detection in single cells.

A hollow Ag/AgCl nanoelectrode for single-cell chloride detection

This work reports the construction of a miniaturized Ag/AgCl nanoelectrode on a nanopipette, which is capable of dual-functions of single-cell drug infusion and chloride detection and is envisioned to promote the study of chloride-correlated therapeutic effects.

Micro-engineering and nano-engineering approaches to investigate tumour ecosystems

The interactions among tumour cells, the tumour microenvironment (TME) and non-tumour tissues are of interest to many cancer researchers. Micro-engineering approaches and nanotechnologies are under extensive exploration for modelling these interactions and measuring them in situ and in vivo to investigate therapeutic vulnerabilities in cancer and extend a systemic view of tumour ecosystems. Here we highlight the greatest opportunities for improving the understanding of tumour ecosystems using microfluidic devices, bioprinting or organ-on-a-chip approaches. We also discuss the potential of nanosensors that can transmit information from within the TME or elsewhere in the body to address scientific and clinical questions about changes in chemical gradients, enzymatic activities, metabolic and immune profiles of the TME and circulating analytes. This Review aims to connect the cancer biology and engineering communities, presenting biomedical technologies that may expand the methodologies of the former, while inspiring the latter to develop approaches for interrogating cancer ecosystems.

The Modification and Applications of Nanopipettes in Electrochemical Analysis

Nanopipette, which is fabricated by glasses and possesses a nanoscale pore in the tip, has been proven to be immensely useful in electrochemical analysis. Numerous nanopipette-based sensors have emerged with improved sensitivity, selectivity, ease of use, and miniaturization. In this minireview, we provide an overview of the recent developments of nanopipette-based electrochemical sensors based on different types of nanopipettes, including single-nanopipettes, self-referenced nanopipettes, dual-nanopipettes, and double-barrel nanopipettes. Several important modification materials for nanopipette functionalization are highlighted, such as conductive materials, macromolecular materials, and functional molecules. These materials can improve the sensing performance and targeting specificities of nanopipettes. We also discuss examples of related applications and the future development of nanopipette-based strategies.

Surface-Roughened SERS-Active Single Silver Nanowire for Simultaneous Detection of Intracellular and Extracellular pHs

The simultaneous and accurate detection of intracellular pH (pH_i) and extracellular pH (pH_e) is essential for studying the complex physiological activities of cancer cells and exploring pH-related therapeutic mechanisms. Here, we developed a super-long silver nanowire-based surface-enhanced Raman scattering (SERS) detection strategy for simultaneous sensing of pH_i and pH_e. A surface-roughened silver nanowire (AgNW) with a high aspect ratio is prepared at a nanoelectrode tip using a Cu-mediated oxidation process, which is then modified by pH-sensitive 4-mercaptobenzoic acid (4-MBA) to form 4-MBA@AgNW as a pH sensing probe. With the assistance of a 4D microcontroller, 4-MBA@AgNW is efficient in simultaneously detecting pH_i and pH_e in both 2D and 3D culture cancer cells by SERS, with minimal invasiveness, high sensitivity, and spatial resolution. Further investigation proves that the surface-roughened single AgNW can also be used in monitoring the dynamic variation of pH_i and pH_e of cancer cells upon stimulation with anticancer drugs or under a hypoxic environment.

Electrochemical Single-Cell Protein Therapeutics Using a Double-Barrel Nanopipette

Single-cell protein therapeutics is expected to promote our in-depth understanding of how a specific protein with a therapeutic dosage treats the cell without population averaging. However, it has not yet been tackled by current single-cell nanotools. We address this challenge by the use of a double-barrel nanopipette, in which one lumen was used for electroosmotic cytosolic protein delivery and the other was customized for ionic evaluation of the consequence. Upon injection of protein DJ-1 through the delivery lumen, upregulation of the antioxidant protein could protect neural PC-12 cells against oxidative stress from phorbol myristate acetate exposure, as deduced by targeting of the cytosolic hydrogen peroxide by the detecting lumen. The nanotool developed in this study for single-cell protein therapeutics provides a perspective for future single-cell therapeutics involving different therapeutic modalities, such as peptides, enzymes and nucleic acids.

Construction and Application of DNAzyme-based Nanodevices

The development of stimuli-responsive nanodevices with high efficiency and specificity is very important in biosensing, drug delivery, and so on. DNAzymes are a class of DNA molecules with the specific catalytic activity. Owing to their unique catalytic activity and easy design and synthesis, the construction and application of DNAzymes-based nanodevices have attracted much attention in recent years. In this review, the classification and properties of DNAzyme are first introduced. The construction of several common kinds of DNAzyme-based nanodevices, such as DNA motors, signal amplifiers, and logic gates, is then systematically summarized. We also introduce the application of DNAzyme-based nanodevices in sensing and therapeutic fields. In addition, current limitations and future directions are discussed.

Functional nucleic acid engineered double-barreled nanopores for measuring sodium to potassium ratio at single-cell level

The use of double-barreled nanopipette (θ-nanopipette) to electrically sample, manipulate, or detect biomaterials has recently seen strong growth in single-cell studies, driven by the potential of the nanodevices and applications that they may enable. Considering the pivotal roles of Na/K ratio (R_Na/K) at cellular level, herein we describe an engineered θ-nanopipette for measuring single-cell R_Na/K. The two independently addressable nanopores, located within one nanotip, allow respective customization of functional nucleic acids but simultaneous deciphering of Na and K levels inside a single cell of a non-Faradic manner. Two ionic current rectification signals, corresponding to the Na- and K-specific smart DNA responses, could be easily used to derive the R_Na/K. The applicability of this nanotool is validated by practical probing intracellular R_Na/K during the drug-induced primary stage of apoptotic volume decrease. Especially, the R_Na/K has been shown by our nanotool to be different in cell lines with different metastatic potential. This work is expected to contribute to futuristic study of single-cell R_Na/K in various physiological and pathological processes.

Greenificated Molecularly Imprinted Materials for Advanced Applications

Molecular imprinting technology (MIT) produces artificial binding sites with precise complementarity to substrates and thereby is capable of exquisite molecular recognition. Over five decades of evolution, it is predicted that the resulting host imprinted materials will overtake natural receptors for research and application purposes, but in practice, this has not yet been realized due to the unsustainability of their life cycles (i.e., precursors, creation, use, recycling, and end-of-life). To address this issue, greenificated molecularly imprinted polymers (GMIPs) are a new class of plastic antibodies that have approached sustainability by following one or more of the greenification principles, while also demonstrating more far-reaching applications compared to their natural counterparts. In this review, the most recent developments in the delicate design and advanced application of GMIPs in six fast-growing and emerging fields are surveyed, namely biomedicine/therapy, catalysis, energy harvesting/storage, nanoparticle detection, gas sensing/adsorption, and environmental remediation. In addition, their distinct features are highlighted, and the optimal means to utilize these features for attaining incredibly far-reaching applications are discussed. Importantly, the obscure technical challenges of the greenificated MIT are revealed, and conceivable solutions are offered. Lastly, several perspectives on future research directions are proposed.

Chiral molecular imprinting-based SERS detection strategy for absolute enantiomeric discrimination

Chiral discrimination is critical in environmental and life sciences. However, an ideal chiral discrimination strategy has not yet been developed because of the inevitable nonspecific binding entity of wrong enantiomers or insufficient intrinsic optical activities of chiral molecules. Here, we propose an "inspector" recognition mechanism (IRM), which is implemented on a chiral imprinted polydopamine (PDA) layer coated on surface-enhanced Raman scattering (SERS) tag layer. The IRM works based on the permeability change of the imprinted PDA after the chiral recognition and scrutiny of the permeability by an inspector molecule. Good enantiomer can specifically recognize and fully fill the chiral imprinted cavities, whereas the wrong cannot. Then a linear shape aminothiol molecule, as an inspector of the recognition status is introduced, which can only percolate through the vacant and nonspecifically occupied cavities, inducing the SERS signal to decrease. Accordingly, chirality information exclusively stems from good enantiomer specific binding, while nonspecific recognition of wrong enantiomer is curbed. The IRM benefits from sensitivity and versatility, enabling absolute discrimination of a wide variety of chiral molecules regardless of size, functional groups, polarities, optical activities, Raman scattering, and the number of chiral centers.

Robotic Intracellular Electrochemical Sensing for Adherent Cells

Nanopipette-based observation of intracellular biochemical processes is an important approach to revealing the intrinsic characteristics and heterogeneity of cells for better investigation of disease progression or early disease diagnosis. However, the manual operation needs a skilled operator and faces problems such as low throughput and poor reproducibility. This paper proposes an automated nanopipette-based microoperation system for cell detection, three-dimensional nonovershoot positioning of the nanopipette tip in proximity to the cell of interest, cell approaching and proximity detection between nanopipette tip and cell surface, and cell penetration and detection of the intracellular reactive oxygen species (ROS). A robust focus algorithm based on the number of cell contours was proposed for adherent cells, which have sharp peaks while retaining unimodality. The automated detection of adherent cells was evaluated on human umbilical cord vein endothelial cells (HUVEC) and NIH/3T3 cells, which provided an average of 95.65% true-positive rate (TPR) and 7.59% false-positive rate (FPR) for in-plane cell detection. The three-dimensional nonovershoot tip positioning of the nanopipette was achieved by template matching and evaluated under the interference of cells. Ion current feedback was employed for the proximity detection between the nanopipette tip and cell surface. Finally, cell penetration and electrochemical detection of ROS were demonstrated on human breast cancer cells and zebrafish embryo cells. This work provides a systematic approach for automated intracellular sensing for adherent cells, laying a solid foundation for high-throughput detection, diagnosis, and classification of different forms of biochemical reactions within single cells.

A High Spatiotemporal Iontronic Single-Cell Viscometer

Ideal single-cell viscometer has remained unachieved, leaving a gap in current palette of single-cell nanotools. Information of single-cell viscosity could contribute to our knowledge of fundamental biological processes, e.g., mass diffusion, biochemical interaction, and cellular responses to many diseases and pathologies. Although advances have been made to this end, existing methods generally suffer from limitations, e.g., low spatiotemporal resolution. Here, we describe a high spatiotemporal iontronic single-cell viscometer that operates upon a patch clamp integrated with double-barreled nanopores separated by a septum of ca. 32 nm. The system enables reversible electroosmotic manipulation of the adjacent small fluid bridging two nanopores, the viscous alternation of which could be sensitively monitored by the ionic responses. In practical cellular studies, significantly, our findings reveal not only the less deviated medium viscosities than those of lysosomes and mitochondria but also the highest viscosities in the near-nuclear region than those of mitochondrion-dense and lysosome-dense regions. This work has provided an accessible single-cell viscometer and enriched the armory of single-cell nanotools.

Recent Advances in Self-Assembled DNA Nanostructures for Bioimaging

DNA nanotechnology has been proven to be a powerful platform to assist the development of imaging probes for biomedical research. The attractive features of DNA nanostructures, such as nanometer precision, controllable size, programmable functions, and biocompatibility, have enabled researchers to design and customize DNA nanoprobes for bioimaging applications. However, DNA probes with low molecular weights (e.g., 10-100 nt) generally suffer from low stability in physiological buffer environments. To improve the stability of DNA nanoprobes in such environments, DNA nanostructures can be designed with relatively larger sizes and defined shapes. In addition, the established modification methods for DNA nanostructures are also essential in enhancing their properties and performances in a physiological environment. In this review, we begin with a brief recap of the development of DNA nanostructures including DNA tiles, DNA origami, and multifunctional DNA nanostructures with modifications. Then we highlight the recent advances of DNA nanostructures for bioimaging, emphasizing the latest developments in probe modifications and DNA-PAINT imaging. Multiple imaging modules for intracellular biomolecular imaging and cell membrane biomarkers recognition are also summarized. In the end, we discuss the advantages and challenges of applying DNA nanostructures in bioimaging research and speculate on its future developments.