Unidirectional transport of both wettable and nonwettable liquids on an asymmetrically concave structured surface.

Unidirectional liquid transport (UDLT) has been widely used in various fields as an important process for transferring both mass and energy. However, UDLT driven by a structural gradient has been witnessed for a long time only in wettable liquids. For nonwettable liquids, UDLT can hardly proceed merely by a structural gradient. Herein, we propose an asymmetrically concave structured surface (AMC-surface), featuring tip-to-base periodically arranged pyramid-shaped concave structures with a certain degree of overlap, which enables the UDLT of both wettable and nonwettable liquids. For wettable liquids, the capillary force along each corner leads to the UDLT pointing toward the base side of the concave pyramid, while for nonwettable liquids, the UDLT is attributable to the static liquid pressure overwhelming the repulsive Laplace pressure induced by the asymmetric grooves and overlapping part. As a result, both wettable and nonwettable liquids transport spontaneously and unidirectionally on the AMC-surface with no energy input. Moreover, the concave structure endows good mechanical stability and can be easily prepared using a facile nail-punching approach over a large area. We also demonstrated its application in a continuous chemical reaction in a confined area. We envision that the unique UDLT behavior on the as-developed AMC-surface will shed new light on the programmable manipulation of various liquids.

Bioinspired Superhydrophobic Fibrous Materials.

Natural fibers with robust water repellency play an important role in adapting organisms to various environments, which has inspired the development of artificial superhydrophobic fibrous materials with applications in self-cleaning, antifogging, water harvesting, heat exchanging, catalytic reactions, and microrobots. However, these highly textured surfaces (micro/nanotextured) suffer from frequent liquid penetration in high humidity and abrasion-induced destruction of the local environment. Herein, bioinspired superhydrophobic fibrous materials are reviewed from the perspective of the dimension scale of fibers. First, the fibrous dimension characteristics of several representative natural superhydrophobic fibrous systems are summarized, along with the mechanisms involved. Then, artificial superhydrophobic fibers are summarized, along with their various applications. Nanometer-scale fibers enable superhydrophobicity by minimizing the liquid-solid contact area. Micrometer-scale fibers are advantageous for enhancing the mechanical stability of superhydrophobicity. Micrometer-scale conical fibrous structures endow a Laplace force with a particular magnitude for self-removing condensed tiny dewdrops in highly humid air and stably trapping large air pockets underwater. Furthermore, several representative surface modification strategies for constructing superhydrophobic fibers are presented. In addition, several conventional applications of superhydrophobic systems are presented. It is anticipated that the review will inspire the design and fabrication of superhydrophobic fibrous systems.

Bioinspired Robust Water Repellency in High Humidity by Micro-meter-Scaled Conical Fibers: Toward a Long-Time Underwater Aerobic Reaction.

Superhydrophobic surfaces have suffered from being frequently penetrated by micro-/nano-droplets in high humidity, which severely deteriorates their water repellency. So far, various biological models for the high water repellency have been reported, which, however, focused mostly on the structural topology with less attention on the dimension character. Here, we revealed a common dimension character of the superhydrophobic fibrous structures of both Gerris legs and Argyroneta abdomens, featured as the conical topology and the micro-meter-scaled cylindrical diameter. In particular, it can be expressed by using a parameter of rp/l > 0.75 µm (r, l, and p are the radius, length, and apex spacing between fibers, respectively). Drawing inspiration, we developed a superhydrophobic micro-meter-scaled conical fiber array with a rather high rp/l value of 0.85 µm, which endows ultra-high water repellency even in high humidity. The micro-meter-scale asymmetric confined space between fibers enables generating a big difference in the Laplace pressure enough to propel the condensed dews away, while the tips help pin the air pocket underwater with a rather long life over 41 days. Taking advantage, we demonstrated a sustainable underwater aerobic reaction where oxygen was continuously supplied from the trapped air pocket by a gradually diffusing process. As a parameter describing both the dimension character and structural topology, the rp/l offers a new perspective for fabricating superhydrophobic fibrous materials with robust water repellency in high humidity, which inspires the innovative underwater devices with a robust anti-wetting performance.

Ultrafast Self-Propelled Directional Liquid Transport on the Pyramid-Structured Fibers with Concave Curved Surfaces.

Self-propelled directional liquid transport (SDLT) has been observed on many natural substrates, serving as an efficient strategy to utilize surrounding liquids for a better habitat to the local environment. Drawing inspiration, various artificial materials capable of SDLT have been developed. However, the liquid transport velocity is normally very low (ca. 3-30 µm/s), which limits its practical applications. Herein, we developed novel pyramid-structured fibers with concave curved surfaces (P-concave curved-fiber, PCCF), which enable the ultrafast SDLT. Specifically, the liquid transport velocity can be up to ∼28.79 mm/s on a dry tri-PCCF, over 50 times faster than that on the surface of Sarracenia trichome (∼520 µm/s). The velocity is even faster on a wet fiber by two times (∼47.34 mm/s). Here, the Laplace pressure difference (FL) induced by the tapered structure determines the liquid transport direction. It is proposed that both the capillary rises imparted by the concave curved surfaces and the oriented microridges/valleys and the enhanced FL aroused by the reduced cross-sectional area accelerate the SDLT on surfaces of the PCCFs. Consequently, the PCCF takes a different liquid transport strategy with a convex-shaped advancing meniscus, differing from that on traditional conical fibers. Moreover, the as-developed PCCF is also applicable for underwater ultrafast SDLT of oil. We envision that the result will open a new perspective for fabricating a fibrous system for microfluidic and liquid manipulation.

A Facile One-Step Approach for Constructing Multidimensional Ordered Nanowire Micropatterns via Fibrous Elastocapillary Coalescence.

Nanowire (NW) based micropatterns have attracted research interests for their applications in electric microdevices. Particularly, aligning NWs represents an important process due to the as-generated integrated physicochemical advantages. Here, a facile and general strategy is developed to align NWs using fibrous elastocapillary coalescence of carbon nanotube arrays (ACNTs), which enables constructing multidimensional ordered NW micropatterns in one step without any external energy input. It is proposed that the liquid film of NW solution is capable of shrinking unidirectionally on the top of ACNTs, driven by the dewetting-induced elastocapillary coalescence of the ACNTs. Consequently, the randomly distributed NWs individually rotate and move into dense alignment. Meanwhile, the aggregating and bundling of ACNTs is helpful to produce carbon nanotube (CNT) yarns connecting neighboring bundles. Thus, a micropatterned NW network composed of a top-layer of horizontally aligned NWs and an under-layer of vertical ACNT bundles connected by CNT yarns is prepared, showing excellent performance in sensing external pressure with a sensitivity of 0.32 kPa-1 . Moreover, the aligned NWs can be transferred onto various substrates for constructing electronic circuits. The strategy is applicable for aligning various NWs of Ag, ZnO, Al2 O3 , and even living microbes. The result may offer new inspiration for fabricating NW-based functional micropatterns.

Multiple functional strategies for amplifying sensitivity of amperometric immunoassay for tumor markers: A review.

Multiple functional strategies have shown great potential in ultrasensitive amperometric immunoassays for tumor markers, which promote conductivity and signal multiple amplification. The sensitivity of amperometric immunoassays is significantly affected by the conductivity and specific area of the sensing interface as well as the electrochemical activity of redox species. Thus, these strategies are generally based on integrating various materials together and endowing immunosensing systems with many advantages, such as large specific area, high electrochemical activity, good conductivity, biocompatibility, and catalytic performance. Owing to the rapid development of functional materials (such as conductive hybrids, catalytic hybrids, enzyme-like materials, highly electrochemical active species, redox nanocomposites, porous materials, hydrogels, and metal-organic framework) and new bioactive substances (including new blocking agents and receptors like peptides and oligonucleotide chains), the sensitivity of related biosensors is usually higher than that of traditional ones, indicating that multiple functional strategies are promising in amperometric immunoassays. Herein, we provide an overview of recent advances in multiple functional strategies that have proven to dramatically enhance the sensitivity of amperometric immunoassays, which incorporate the following materials: (1) conductive nanomaterials hybrids; (2) catalytic nanomaterials hybrids; (3) new redox materials; (4) three-dimensional porous materials; (5) new receptors and blocking agents.

Bovine serum albumin as an effective sensitivity enhancer for peptide-based amperometric biosensor for ultrasensitive detection of prostate specific antigen.

Bovine serum albumin (BSA) was firstly implemented as an effective sensitivity enhancer for a peptide-based amperometric biosensor for the ultrasensitive detection of prostate specific antigen (PSA). A porous and conductive substrate of chitosan-lead ferrocyanide-(poly(diallyldimethylammonium chloride)-graphene oxide) was in-situ generated on a glassy carbon electrode (GCE), in which Pb2[Fe(CN)6] served as a novel redox species with strong current signal at -0.46 V (vs. Ag/AgCl). Poly(diallyldimethylammonium chloride)-graphene oxide was applied to improve conductivity of the substrate. After adsorbing Pb2+ for signal amplification, chitosan provided active sites to simultaneously immobilize peptides and 1-aminopropyl-3-methylimidazolium chloride by glutaraldehyde. To enhance the sensitivity, BSA was chemically linked to the immobilized peptide, behaving as a serious decrease of current signal for BSA hindering the electron transfer. The dramatic increase of current signal of the biosensor was obtained by PSA cleaving the immobilized BSA-peptide. The proposed biosensor exhibited a detection limit of 1fgmL-1 for PSA and its sensitivity was seven-fold higher than previous works.

Multiple signal amplification strategies for ultrasensitive label-free electrochemical immunoassay for carbohydrate antigen 24-2 based on redox hydrogel.

In this work, multiple signal amplification strategies for ultrasensitive label-free electrochemical immunoassay for carbohydrate antigen 24-2 (CA242) were developed using redox sodium alginate-Pb2+-graphene oxide (SA-Pb2+-GO) hydrogel. The SA-Pb2+-GO hydrogel was synthesised by simply mixing SA, GO, and Pb2+ and then implemented as a novel redox species with a strong current signal at -0.46V (vs. Ag/AgCl). After the three-dimensional and porous SA-Pb2+-GO hydrogel was in situ generated on a glassy carbon electrode (GCE), chitosan was adsorbed on the obtained electrode to further enrich Pb2+. When chitosan-Pb2+/SA-Pb2+-GO/GCE was incubated with anti-CA242 using glutaraldehyde and blocked by bovine serum albumin, the immunoassay platform for CA242 was obtained. Owing to the addition of GO, the obtained conductive SA-GO/GCE was beneficial for signal amplification. After incubating SA-GO/GCE with excessive amounts of Pb2+, the resistance of SA-Pb2+-GO/GCE further decreased and a strong redox signal was obtained. The chitosan fixed by electrostatic adsorption resulted in further adsorption of Pb2+, behaving as further amplifying the signal and improving conductivity. In this case, multiple signal amplification strategies were involved in the proposed immunosensor for the ultrasensitive detection of CA242. Under the optimal conditions, the proposed immunosensor exhibited a wide linear range from 0.005UmL-1 to 500UmL-1 with an ultralow detection limit of 0.067mUmL-1. In comparison to previous works, the sensitivity of this method was 32.98µA (log10CCA242)-1, which was a five-fold increase from the previous works.

Triple sensitivity amplification for ultrasensitive electrochemical detection of prostate specific antigen.

In general, current difference (ΔI) due to immunoreactions is significant in determining biosensor sensitivity. In this work, a new strategy of triple sensitivity amplification for ultrasensitive electrochemical detection of prostate specific antigen (PSA) was developed. Au-poly(methylene blue) (Au-PMB) was implemented as a redox species with strong current signal at -0.144V and used to fabricate the substrate of the biosensor. Conductive reduced graphene oxide-Au nanocomposites (Au-rGO) were coated on the Au-PMB modified glassy carbon electrode (GCE) to amplify current signal. After peptides (CEHSSKLQLAK-NH2) were fixed on the Au-rGO/Au-PMB/GCE, the fixed peptides reacted with glutaraldehyde to immobilize polydopamine-Au-horse radish peroxidase nanocomposites (PDA-Au-HRP). The electrochemical sensing interface for PSA was realized. Due to smaller resistance compared to antibodies, the peptides which can be cleaved specifically by PSA were employed. After the incubation of PSA, a large ΔI was obtained and behaved as the decrease of current signal. Then the remaining PDA-Au-HRP accelerated an enzyme-catalyzed precipitation reaction between 4-chloro-1-naphthol and H2O2. A further decrease in current signal (namely the increase in ΔI) resulted from the poorly conductive precipitation adhering onto the biosensor. The designed biosensor presented a wide linear range from 1.0fgmL-1 to 100ngmL-1 with an ultralow detection limit of 0.11fgmL-1.

Ratiometric ultrasensitive electrochemical immunosensor based on redox substrate and immunoprobe.

In this work, we presented a ratiometric electrochemical immunosensor based on redox substrate and immunoprobe. Carboxymethyl cellulose-Au-Pb2+ (CMC-Au-Pb2+) and carbon-Au-Cu2+ (C-Au-Cu2+) nanocomposites were firstly synthesized and implemented as redox substrate and immunoprobe with strong current signals at -0.45 V and 0.15 V, respectively. Human immunoglobulin G (IgG) was used as a model analyte to examine the analytical performance of the proposed method. The current signals of CMC-Au-Pb2+ (Isubstrate) and C-Au-Cu2+ (Iprobe) were monitored. The effect of redox substrate and immunoprobe behaved as a better linear relationship between Iprobe/Isubstrate and Lg CIgG (ng mL-1). By measuring the signal ratio Iprobe/Isubstrate, the sandwich immunosensor for IgG exhibited a wide linear range from 1 fg mL-1 to 100 ng mL-1, which was two orders of magnitude higher than other previous works. The limit of detection reached 0.26 fg mL-1. Furthermore, for human serum samples, the results from this method were consistent with those of the enzyme linked immunosorbent assay (ELISA), demonstrating that the proposed immunoassay was of great potential in clinical diagnosis.