Outer-Surface Functionalized Solid-State Nanochannels for Enhanced Sensing Properties: Progress and Perspective.

Solid-state nanochannel-based sensing systems have been established as vigorous tools for sensing plentiful biomarkers due to their label-free, highly sensitive, and high-throughput screening. However, research on solid-state nanochannels has predominantly centered on the functional groups modified on the inner wall, neglecting investigations into the outer surface. Actually, the outer surface, as a part of the nanochannels, also plays a key role in regulating ionic current. When the target nears the entrance of the nanochannel and prepares to pass through, it would also interact with functional groups located on the nanochannel's outer surface, leading to subsequent alterations in the ionic current. Recently, the probes on the outer surface have experimentally demonstrated their ability to independently regulate ionic current, unveiling advantages in in situ target detection, especially for targets larger than the diameter of the nanochannels that cannot pass through them. Here, we review the progress over the past decade in nanochannels featuring diverse outer-surface functionalization aimed at enhanced sensing performance, including charge modification, wettability adjustment, and probe immobilization. In addition, we present the promises and challenges posed by outer-surface functionalized nanochannels and discuss possible directions for their future deployments.

Fluorescent Selectivity-Enhanced FRET Based on 3D Photonic Crystals for Multianalyte Sensing.

Fluorescence resonance energy transfer (FRET) finds widespread utility in biochemical sensing, single-molecule experiments, cell physiology, and various other domains due to its inherent simplicity and high sensitivity. Nevertheless, the efficiency of energy transfer between the FRET donor and acceptor is significantly contingent on the local photonic environment, a factor that limits its application in complex systems or multianalyte detections. Here, a fluorescent selectivity-enhanced acridine orange (AO)-aflatoxins (AFs) FRET system based on a range of 3D topological photonic crystals (PCs) was developed with the aim of enhancing the selectivity and discrimination capabilities of FRET. By exploring the angle-dependent characteristics of the photonic stopband, the stopband distribution across different 3D topological PCs pixels was investigated. This approach led to selective fluorescence enhancement in PCs that matched the stopbands, enabling the successful discrimination of six distinct aflatoxins and facilitating complex multianalysis of moldy food samples. In particular, the stopband, which was strategically positioned within the blue-purple structural color range, exhibited a strong alignment with the fluorescence peaks of both the FRET donor and acceptor. This alignment allowed the 3D three-pointed star PCs to be effectively employed for the identification of mixed samples containing six distinct aflatoxins as well as the detection of real aflatoxin samples present in moldy potatoes, bread, oats, and peanuts. Impressively, this approach achieved a remarkable accuracy rate of 100%. This innovative strategy not only presents a novel avenue for developing a multitarget discrimination analysis system but also offers a convenient pretreatment method for the quantitative detection of various aflatoxins.

Solid-state nanochannels for bio-marker analysis.

Bio-markers, such as ions, small molecules, nucleic acids, peptides, proteins and cells, participate in the construction of living organisms and play important roles in biological processes. It is of great significance to accurately detect these bio-markers for studying their basic functions, the development of molecular diagnosis and to better understand life processes. Solid-state nanochannel-based sensing systems have been demonstrated for the detection of bio-markers, due to their rapid, label-free and high-throughput screening, with high sensitivity and specificity. Generally, studies on solid-state nanochannels have focused on probes on the inner-wall (PIW), ignoring probes on the outer-surface (POS). As a result, the direct detection of cells is difficult to realize by these inner-wall focused nanochannels. Moreover, the sensitivity for detecting ions, small molecules, nucleic acids, peptides and proteins requires further improvement. Recent research has focused on artificial solid-state nanochannels with POS, which have demonstrated the ability to independently regulate ion transport. This design not only contributes to the in situ detection of large analytes, such as cells, but also provides promising opportunities for ultra-high sensitivity detection with a clear mechanism. In this tutorial review, we present an overview of the detection principle used for solid-state nanochannels, inner-wall focused nanochannels and outer-surface focused nanochannels. Furthermore, we discuss the remaining challenges faced by current nanochannel technologies and provide insights into their prospects.

Recent Advances in Printable Flexible Optical Devices: From Printing Technology and Optimization Strategies to Perspectives.

Recently, flexible optical devices have triggered booming developments in various research fields, including display equipment, sensors, energy conversion, and so on, due to their high compatibility, portability, and wearability. With the advantages of strong design ability, high precision, and high integration, printing technologies have been recognized as promising methods to realize flexible optical devices. In this Perspective, recent progress on printing strategies for fabricating flexible optical devices are introduced systematically. First, through adjusting the composition of inks, selecting flexible substrates, and controlling external stimulation, fabrication of flexible optical devices based on inkjet printing is illustrated. Then, flexible optical devices fabricated by template-induced printing, 3D printing, slot-die printing, and screen printing are summarized. Finally, prospects and future development directions based on printing technology for flexible optical devices are proposed.

Multi-analyte sensing strategies towards wearable and intelligent devices.

Continuous efforts to produce functional nanomaterials and flexible/stretchable devices have promoted cumbersome, laboratorial, detection processes toward wearable and portable intelligent sensing approaches. Responding to the challenges of the multiple analytes, mixtures, and complex components of practical samples, sensing array and multivariate analysis techniques have a significant advantage in terms of superior analytical capabilities, i.e., they are convenient, rapid, sensitive and have high-throughput for multi-analyte identification in food safety, clinical diagnoses, and environmental monitoring. Besides traditional molecular design and recognition mechanisms, materials with micro/nano structures also contribute to strong signals, sensitive responses, and novel properties. In this review, through a new perspective of signal amplification for responsive discrimination, we summarize progress in developing sensing arrays based on diverse micro/nanomaterials and their integrated devices for multi-analyte discrimination. An overview of strategies for constructing sensing arrays through various micro or nano building blocks, including 0D nanoparticle assembly and modification, 1D nanowires and fibers, 2D graphene and textiles, is schematized. Then, portable and wearable devices integrating colorimetric sensors or flexible electrochemical electrodes with the newest microelectronic units and circuit boards are presented. Meanwhile, the latest artificial intelligence (AI) algorithms are introduced for massive data analysis in complex biological and environmental systems. With future developments in facile and accurate discrimination for multi-analyte research, extended applications will gear up in various fields.

Synergistic Effect of Bio-Inspired Nanochannels: Hydrophilic DNA Probes at Inner Wall and Hydrophobic Coating at Outer Surface for Highly Sensitive Detection.

During the past few decades, bio-inspired nanochannels have been well developed and applied in biosensing, energy transfer, separation, and so on. Here, inspired by the synergistic effect of biological nanopores, biomimetic solid-state nanochannels with hydrophilic DNA probes at the inner wall (DNA@IWHydrophilic ) and hydrophobic coating at the outer surface (None@OSHydrophobic ) are designed. To demonstrate their prompted sensing properties, Hg2+ and its specific probe are selected as target and hydrophilic DNA probes, respectively. Compared with the traditional solid-state nanochannels with hydrophilic probes distributed on both the inner wall and outer surface, the nanochannels with DNA@IWHydrophilic +None@OSHydrophobic significantly decrease the limit of detection (LOD) by 105 -fold. The obvious improvement of sensitivity (with LOD of 1 nM) is attributed to the synergistic effect: None@OSHydrophobic results in the nanochannel's effective diameter decrease and DNA@IWHydrophilic induces a specific sensing target. Meanwhile, nanomolar detection of Hg2+ in human serum and in vivo fish muscle are achieved. Through molecular dynamics simulation, the synergistic effect can be confirmed by ion fluxes increasement; the relative carbon nanotube increases from 135.64% to 135.84%. This work improves the understanding of nanochannels' synergistic effect and provides a significant insight for nanochannels with improved sensitivity.