Abstract A Gemini-like surfactant is formed by connecting short chain dibasic acid and long chain tertiary amine in the molar ratio of 1:2 through the non-covalent action of electrostatic attraction, and does not need complicated synthesis. Due to the tertiary amine group in the Gemini-like surfactant, it exhibits pH-responsive properties. However, in the research, we were pleasantly surprised to find that the Gemini-like surfactants also showed temperature response characteristics. With the increase of temperature, the viscosity of the system increases rapidly, and it is resistant to high temperatures. At 60°C, the zero-shear viscosity of the system at the concertation of 300 mM can reach an extremely high value of 11967.73 Pa·s, which was higher than most of wormlike micelles formed by the conventional covalently linked oligomeric counterparts. The reason for this phenomenon may be that as the temperature increases, the hydrogen bonds in the system are destroyed, resulting in the reduction of the repulsive force between molecules and the shortening of the intermolecular distance, which makes the micelles more entangled closely.

Brain science has remained in the global spotlight as an important field of scientific and technological discovery. Numerous in vitro and in vivo animal studies have been performed to understand the pathological processes involved in brain diseases and develop strategies for their diagnosis and treatment. However, owing to species differences between animals and humans, several drugs have shown high rates of treatment failure in clinical settings, hindering the development of diagnostic and treatment modalities for brain diseases. In this scenario, microfluidic brain-on-a-chip (BOC) devices, which allow the direct use of human tissues for experiments, have emerged as novel tools for effectively avoiding species differences and performing screening for new drugs. Although microfluidic BOC technology has achieved significant progress in recent years, monitoring slight changes in neurochemicals, neurotransmitters, and environmental states in the brain has remained challenging owing to the brain’s complex environment. Hence, the integration of BOC with new sensors that have high sensitivity and high selectivity is urgently required for the real-time dynamic monitoring of BOC parameters. As sensor-based technologies for BOC have not been summarized, here, we review the principle, fabrication process, and application-based classification of sensor-integrated BOC, and then summarize the opportunities and challenges for their development. Generally, sensor-integrated BOC enables real-time monitoring and dynamic analysis, accurately measuring minute changes in the brain and thus enabling the realization of in vivo brain analysis and drug development.

A double-tailed surfactant with two quaternary ammonium head groups forms toroidal micelles, wormlike micelles and vesicles in aqueous solutions. The viscoelasticity of the solution can be significantly enhanced by adding inorganic salts.

A long-tailed surfactant with two quaternary ammonium head groups forms extremely long wormlike micelles in the presence of sodium laurate in aqueous solutions. The solution viscoelasticity is significantly enhanced at low concentrations.

Stimulus-responsive surfactants (N+-C-n-N,n = 14 or 16) can stabilize conventional emulsions, Pickering emulsions and oil-in-dispersion emulsions in the presence of oppositely and similarly charged nanoparticles. Rapid demulsification can be successfully achieved by bubbling CO2. In the presence of CO2, N+-C-n-N becomes a hydrophilic Bola-type surfactant, N+-C-n-NH+, and is an inferior emulsifier either when used alone or together with charged nanoparticles, resulting in demulsification. In addition, nearly all N+-C-n-NH+ molecules are present in the aqueous phase after demulsification without contaminating the oil phase. The aqueous phase can be recycled and used again for further emulsification of oils. Compared with the pH responsive systems, there is no accumulation of salt after the gas cycles, and more cycles can be performed. This protocol is a green process and leads to preparation of various temporarily stable emulsions used in oil emulsion transportation, emulsion polymerization, industrial catalysis, nanomaterial synthesis and other fields. (C) 2022 Elsevier B.V. All rights reserved.

Metal-organic frameworks（MOFs）, a crystalline porous material with a periodic network structure formed by the self-assembly of transition metal ions and organic ligands, have been widely applied in various fields due to their rich composition and structural diversity. Among various types of MOFs, stimuli-responsive MOFs have gained increasing attention in recent years,because of their broad application in the field of physics, biology, and chemistry. In this review, we analyzed and classified the mechanism of stimulus-response MOFs（p H response, glucose response,GSH response, light response, temperature response） and their applications in drug delivery,adsorption and luminescence functions, magnetization and catalysis functions, probe and sensor.

Amyloid-β oligomer (AβO) is believed to cause neurotoxicity which is linked to Alzheimer's disease (AD). Therefore, the detection of AβO has been proposed as an effective method for the early diagnosis of AD. In this work, several three-dimensional layers using gold nanoparticles (AuNPs) embedded in different conducting polymer matrix, including poly (thiophene-3-acetic acid), poly (pyrrole-2-carboxylic acid), and poly (pyrrole-3-carboxylic acid), were harnessed as transducers for the large surface area and high electrical conductivity. The cellular prion protein (PrPC) was utilized as the biorecognition element for the specific detection of AβO. The prepared electrochemical sensors were fabricated and compared afterward, in terms of sensitivity and detection range for the highly sensitive detection of AβO. In comparison, the PrPC/AuNPs embedded in Ppy-3-COOH matrix (AuNPs-E-Ppy-3-COOH matrix) was demonstrated to have higher sensitivity and wider detection range (10−9 to 103 nM). Subsequently, through the ex vivo real sample analysis within cerebrospinal fluid and blood test, it is proved that PrPC/AuNPs-E-Ppy-3-COOH matrix can be used for the early diagnosis of AD.

A pH-switchable wormlike micellar system with high viscoelasticity was prepared by mixing N-(3(dimethylamino) propyl) stearamide (SAM) and phthalic acid (PA) at the molar ratio of 2:1. By simple in situ neutralization reaction, SAM and PA could dynamically combine to fabricate a pseudooligomeric surfactant without additional inorganic salts. Through the results of surface activity, rheology and Small-angle X-ray scattering (SAXS), it was found that the pseudo-oligomeric surfactant was readily to form viscoelastic wormlike micelles and showed remarkable thickening ability. The maximum zero shear viscosity (eta(o)) was up to 9.4 x 10(3) Pa.s, which was higher than most of wormlike micelles formed by the conventional covalently linked oligomeric counterparts. The viscoelastic fluid formed by the pseudo-oligomeric surfactant was highly sensitive to pH, whose viscosity could be decreased to 0.001 Pa.s instantly by adding a small amount of acid or alkali. (C) 2021 Elsevier B.V. All rights reserved.

A tetrameric monomer containing an azobenzene group (abbreviated as tetra-N(AZO)-Br) was synthesized in this paper, and a “pseudo” oligomeric surfactant was constructed using tetra-N(AZO)-Br and a traditional surfactant, sodium oleate (SO), by non-covalent bonded interaction. The synthesized tetra-N(AZO)-Br was characterized by 1H NMR and UV–Vis spectra. The viscoelasticity and the difference in nuclear magnetic resonance (NMR) and ultraviolet (UV) absorption of the SO/tetra-N(AZO)-Br “quasi” tetrameric surfactant solution at different concentrations were investigated. The SO/tetra-N(AZO)-Br “pseudo” tetrameric surfactant could form highly viscoelastic worm-like micelles in solution, and the zero-shear viscosity of the system increased with increasing concentration. The viscoelastic properties of SO/tetra-N(AZO)-Br “pseudo” tetrameric surfactant had no obvious change after UV light irradiation. Since the combination of SO and tetra-N(AZO)-Br molecules was in dynamic equilibrium through the attraction of positive and negative charges, as much as 30% of the trans-tetra-N(AZO)-Br molecules in worm-like aggregates were transformed to their cis- structure. The un-transformed trans-tetra-N(AZO)-Br molecule could move in the aggregate and help maintain the structure of the aggregates, so that the viscosity had no obvious change.

Silica nanoparticles are riot surface active due to their strong hydrophilicity. However, the negatively charged silica nanoparticles in aqueous media can be in situ surface activated by adsorbing cationic surfactant molecules and thereby aggregate to oil/water interface to stabilize emulsions. In this paper, the in situ surface activation effects of three water soluble cationic surfactants of different structures, cetyltrimethylammonium bromide (CTAB) with single headgroup and single chain, didodecyldimethylammonium bromide (di-C(12)DMAB) with single headgroup and double chains, and trimethylene-di (tetradecacyloxyethyldimethyl ammonium bromide) (II-14-3), a Gemini cationic surfactant with double headgroups and double chains, were examined by characterizing the formation, stability and phase inversion of n-octane-water emulsions, and the relative mechanisms were explored by measuring zeta potentials, adsorption isotherms, and contact angles etc. The results show that a monolayer formation at particle/water interface with hydrophobic tail toward water, which transits the wettability of the particle from strongly hydrophilic to partially hydrophilic and partially hydrophobic, is responsible for the in situ surface activation. By adsorbing CTAB or II-14-3 the hydrophobicity of particles is appropriately enhanced so that they can stabilize n-octane-in-water[O/W(1)] emulsion, whereas by adsorbing di-C(12)DMAB a much denser monolayer can be formed which endows particles a hydrophobicity so strong that the O/W(1) emulsion can be inverted to W/O type. At high surfactant concentration double layer adsorption occurs at particle-water interface and particles are returned to hydrophilic and thus lose their surface activity, while the free surfactant concentration in aqueous phase is high enough to stabilize O/W(2) emulsion solely. Thus an O/W(1)-> W/O -> O/W(2) double phase inversion can be induced by simply increasing surfactant concentration for the emulsion stabilized by a mixture of silica nanoparticles and di-C(12)DMAB.