Metal oxide nanocrystals/mesoporous carbon composite materials are promising in the energy storage field. However, the construction of stoichiometric ternary nanocrystals-functionalized mesoporous carbon materials remains a great challenge. Herein, the synthesis of ultradispersed and ultrasmall LiTiO2 nanocrystals/ordered mesoporous carbon composites via a chelation-mediated multicomponent coassembly strategy is reported. In this case, the self-assembly into ordered mesostructures and the crystallization of nanoparticle processes can be decoupled by the molecular chelate strategy where citrate ligands can effectively inhibit the hydrolysis and phase separation of metal oxide precursors and confine the crystallization into nanocrystals without aggregation. The obtained 33%-LiTiO2–OMC composites present a high specific surface area (≈912 m2 g−1), a large pore volume (≈0.62 cm3 g−1), a uniform pore size (≈4.1 nm), and ultradispersed LiTiO2 nanocrystals (≈3 nm). When loading 60% sulfur, the composites exhibit a high reversible capacity (966 mAh g−1 after 100 cycles at 0.5C), an excellent rate capacity (700 mAh g−1 at 5C), and a long-term cycling performance (63% retention after 1000 cycles at 5C). This method is very simple and reproducible, which paves a new way for the design and synthesis of functional mesoporous materials.

The bar-coating technique for perovskite solar cells has been studied as a scalable process in relation to solar cell commercialization. In large-area bar coating, solvents with the high boiling points like dimethylformamide or γ-butyrolactone have difficulty in obtaining uniform and planar film at room temperature as they have slow evaporation rate. As an alternative, 2-methoxyethanol is a volatile and polar solvent, which is useful on a bar coating if applied using an air-blowing method with an air knife. Herein, a hot gas-blowing method for the fabrication of a perovskite layer to achieve both proper solvent evaporation and high crystallinity is developed. With 75 °C of N2 blowing on the bar-coated perovskite solution, highly crystalline perovskite films with large grains without voids are fabricated, showing excellent optical and electrical characteristics, such as long carrier lifetime, few carrier recombinations, and low trap density. Both small-area solar cells and large-area modules show good performance, 20.85% for the solar cell and 15.4% for the solar module. The results indicate that the newly proposed method can equally be applied to the fabrication of large-area solar cells toward commercialization.

Recently, electronics research has made major advances toward a new platform technology facilitating form factor-free devices. 3D printing techniques have attracted significant attention in the context of fabricating arbitrarily shaped circuits. Herein, a 3D-printable metallic ink comprising multidimensional eutectic gallium indium (EGaIn)/Ag hierarchical particles is proposed to fabricate arbitrarily designable solid/liquid biphasic conductors that can be inherently self-healed/chip bonded and do not suffer from liquid flood out due to their liquid and solid nature, respectively. The EGaIn/Ag hierarchical particles are designed to have plasmonic optical absorption at the visible green–red wavelength regime, which is elucidated by an optical simulation study, and also enable the direct transfer of thermal energy, generated in the vicinity of the Ag nanoparticles, to the surface of the EGaIn particles. The 3D surface conformal green laser irradiation process activates the evolution of the biphasic conductive layer from the as-printed insulating particulate one. The chemical/physical evolution is elucidated along with a photothermal simulation study for clarifying the suppression of undesirable side reactions. It is demonstrated that the biphasic conductors formed by successive 3D printing and the surface conformal green laser irradiation process exhibit electrical properties that have thus far been unexplored in solid metallic conductors.

Wax chemistry, especially long-chain aldehydes, and surface wettability are discussed to have a stimulating effect on the development of Blumeria graminis, the pathogen of powdery mildew on wheat. Here, these specific surface properties are investigated on leaves of different wheat varieties and on developed test systems coated with plant wax and wax components. So far, the wettability of leaves has not been achieved by artificial substrates used in in vitro studies. With the test systems developed here, a wettability comparable to that on leaf surfaces and the signal character of wax chemistry could be investigated individually and in combination. The results show that wax morphology and chemistry (analyzed by scanning electron microscopy and gas chromatography) as well as wettability of leaves have no differences that would suggest a relationship with variety susceptibility. Furthermore, the influence of wax chemistry and wettability on the process of prepenetration of B. graminis on leaves and test systems is investigated. Germination and differentiation are not stimulated on any of the test systems compared to surfaces without the signals offered. Wettability, wax chemistry, and components such as long-chain aldehydes could not be identified as decisive signals for the germination development of B. graminis.

Vanadium oxides are highly valued as electrochromic materials because of their multicolor capabilities. However, their practical applications have been limited due to challenges such as the dissolution of vanadate into aqueous electrolytes, leading to poor long-term stability. Herein, a solution is proposed to the vanadate dissolution issue by utilizing a hybrid electrolyte consisting of tetraethylene glycol dimethyl ether (TEGDME) and water. This electrolyte has the unique ability to form a robust cathode electrolyte interface layer on vanadium oxide electrodes. As a proof of concept, zinc-anode-based multicolor transparent electrochromic displays are prepared using layered potassium vanadate (K2V6O16·1.5H2O, KVO) with a TEGDME–water hybrid electrolyte. By soaking the KVO electrode in the hybrid electrolyte, it is demonstrated that KVO has remarkable stability against dissolution. Furthermore, it is shown that KVO has superior electrochromic performance compared to sodium vanadate (NaV3O8·1.5H2O, SVO), due to the wide KVO interlayer spacing. Given the enhanced performance of this hybrid electrolyte and KVO cathode material, a zinc-anode-based electrochromic display prototype is shown to exhibit compelling performance. As such, this work is expected to be a significant catalyst for accelerating the development of vanadate-based electrochromic displays.

Sensing bioelectrical signals is of great significance to understand human disease. Reliable bioelectronic interface is the guarantee of high-quality bioelectrical signals. The unique electrochemical property and the mixed ionic and electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) make it an ideal material for the skin/tissue–electronic interface. However, pristine PEDOT:PSS-based devices cannot meet the requirements for practical use. Toward this end, herein, the development of PEDOT:PSS-based electrodes and their most recent advances in sensing bioelectrical signals are summarized. First, the generation mechanism of bioelectrical signals is introduced in detail. Then, according to the characteristics of bioelectrical signals, the requirements of bioelectrodes are discussed. Next, representative achievements for improving conductivity, stretchability, and stability of PEDOT:PSS are introduced. Bioelectrical signals such as electromyogram (EMG), electrocardiogram (ECG), electrooculogram (EOG), and electroencephalogram (EEG) are successfully recorded by these PEDOT:PSS-based electrodes. Finally, a brief summary is provided, and the opportunities and challenges are also discussed.

The photovoltaic (PV) performance of perovskite solar cells (PSCs) has rapidly advanced in the recent years; yet, the stability issue remains one of the last-mile challenges on the road to commercialization. Charge transport layers and their interfaces with perovskites stand for critical tuning knobs that determine the device stability of PSCs. This review focuses on the effects of modification of SnO2 electron transport layers (ETLs) on the interfacial physicochemical properties and stability of PSC devices. In detail, the intrinsic defects, surface hydroxyls, and nonuniform morphology of SnO2 will negatively impact its interfacial physicochemical properties, thus degrading the device stability of PSCs. To tackle these existing issues, three modification approaches, such as surface morphology control, surface physicochemical modifications, and surface composite-structure design, are categorized. Lastly, future perspectives in further promoting the stability of PSCs from SnO2 ETLs are raised based on the currently unresolved issues from both material and device levels.

Complexes associated with strong electrostatic interactions constitute a valuable method to construct tough hydrogels, but current systems are either unstable in saline environments or lead to relatively soft matrices. Herein, a class of acid-base complex (ABC) hydrogels made from poly(2-(dimethylamino)ethyl methacrylate) and glassy poly(methacrylic acid) (PMA) is reported. The tough hydrogels are prepared via a dialysis-free process and maintain their structure in saline solutions. Results indicate that the glassy feature of PMA endows the ABC hydrogels with high moduli (227 MPa), typical yielding points (3 MPa), and moderate stretchability (300% strain). The glassy backbones (PMA chains) are stiff at low temperatures, and would be melted at high temperatures, which bring about interesting shape-memory effects and inverse memory-forgetting behaviors. These results may inspire a simple but powerful strategy to design innovative hydrogel materials.

Due to the direct conversion between thermal and electrical energy, thermoelectric materials and their devices exhibit great potential for power generation and refrigeration. With the rapid development of personal wearable electronics, the design of flexible inorganic thermoelectric materials and devices receives increasing attention. As one of the most mature thin-film fabrication techniques, magnetron sputtering plays a key role in the fabrication of inorganic thermoelectric thin films and devices, but its progress is still not timely and comprehensively reviewed. Herein, recent advances in magnetron sputtering-fabricated thermoelectric materials and devices are studied, including their thermoelectric properties, mechanical properties, and device design routes. The differences in the properties of thermoelectric materials under different sputtering conditions, as well as their underlying mechanisms, are carefully discussed. In the end, it is pointed out the challenges and future directions for magnetron sputtering-prepared inorganic thermoelectric thin-film materials and devices for practical applications. This review can serve as a useful reference to guide the design of inorganic thermoelectric materials and devices prepared by magnetron-sputtering-based deposition techniques.

With growing demands for portable electronics, flexible aqueous energy storage devices such as supercapacitors and Zn-based batteries have drawn tremendous interest from both academic and industrial fields. Organo-hydrogels, crosslinked amphiphilic polymers filled with organic solvents and water, are regarded as an ideal electrolyte candidate for portable electronic applications, especially due to their superior environmental adaptation. Organo-hydrogels can reserve the advantages of the corresponding hydrogels and achieve some unique features such as broad temperature tolerance, high mechanical stability, strong interfacial interaction, and decent ionic conductivity. This review outlines the composition fundamentals, preparation methods, and comprehensive properties of reported organo-hydrogel electrolytes. In particular, supercapacitors and Zn-based batteries that operate under harsh temperature conditions and unusual mechanical deformations endowed by organo-hydrogel electrolytes are further highlighted. Moreover, a unique perspective on the current challenges and future development directions of the organo-hydrogel electrolytes for flexible energy storage is also provided.

The photo-rechargeable supercapacitor enables the self-powering of flexible wearable electronics. However, flexible wearable electronics require supercapacitors not only with excellent flexibility but also with high energy density. P-diaminoazobenzene (P-Azo) as a new type of organic electrode material with NN is directly connected to the benzene ring and forms a large π-conjugated system, which makes it have a lower lowest unoccupied molecular orbital (LUMO) energy level, is beneficial to transfer of electrons, and increases the conductivity of organic molecules. In addition, NN can realize the transfer of two electrons, which makes P-Azo have a higher energy density. Asymmetric flexible supercapacitors are fabricated by assembling P-Azo, activated carbon, and an adhesive electrolyte, with 425.2 mW h cm−2 (55.19 Wh kg−1) energy density at a power density of 80 mW cm−2 (10.38 W kg−1), and 90.7% capacitance retention after 80 000 cycles of bending. In this work, supercapacitors and perovskite submodules are coupled to prepare a photo-rechargeable supercapacitor to achieve a 7% overall energy-conversion efficiency. Therefore, this supercapacitor paves a practical route for powering future wearable electronics.

Understanding changes in the mechanical features of a single protein from a mutated virus while establishing its relation to the point mutations is critical in developing new inhibitory routes to tackle the uncontrollable spread of the virus. Addressing this, herein, the chemomechanical features of a single spike protein are quantified from alpha, beta, and gamma variants of SARS-CoV-2. Integrated amplitude-modulation atomic force microscopy is used with dynamic force–distance curve (FDC) spectroscopy, in combination with theoretical models, to quantify Young's modulus, stiffness, adhesion forces, van der Waals forces, and the dissipative energy of single spike proteins. These obtained nanomechanical properties can be correlated with mutations in the individual proteins. Therefore, this work opens new possibilities to understand how the mechanical properties of a single spike protein relate to the viral functions. Additionally, single-protein nanomechanical experiments enable a variety of applications that, collectively, may build up a new portfolio of understanding protein biochemistry during the evolution of viruses.

The quest to develop efficient electrocatalysts for water-splitting is still an ongoing challenge. Intense efforts have been dedicated over the years to design effective methods to improve the electrocatalytic performances. In recent times, the single-source (molecular) precursor (SSP) approach has gained enormous attention from the scientific community as it operates at low temperatures and leads to the formation of unique nanostructured materials, with fine-tuned chemical and physical properties, resulting in high and stable catalytic activities. Herein, the recent developments in molecule-to-material chemistry and their applications toward the oxygen evolution reaction, hydrogen evolution reaction, and overall water-splitting are summarized. Furthermore, the review focuses on understanding the reconstruction process of the SSP-derived materials and the adopted techniques (in situ and ex situ) to obtain insights into the active structures for catalysis. The future possibilities of applying these materials for value-added organic electro-oxidation/reduction reactions are also explored.

The development of water-soluble aggregation-induced emission luminogens (AIEgens) emitting in the near-infrared (NIR) window holds promise for efficient biomedical applications. Nevertheless, synthesizing water-soluble counterparts of NIR AIEgens presents difficulties due to their intrinsic hydrophobic properties. To address this issue, researchers have developed various molecular design strategies to improve the water solubility of NIR AIEgens. The integration of hydrophilic groups and targeting moieties is a crucial aspect of achieving precise phototheranostics. Here, diverse approaches to attain water-soluble NIR AIEgens for biomedical applications are presented, and three commonly used strategies that involve decorating NIR AIEgens with positively or negatively charged groups, hydrophilic chains, and bioactive moieties are elaborated. These rational design strategies are believed to provide solutions for enhancing the water solubility and biological performance of NIR AIEgens in a single action. The remaining challenges and opportunities in this field are also discussed. The aim is to provide new insights into the design of water-soluble NIR AIEgens and inspire more researchers to make significant contributions to this promising research area.

Solutions for improving fast charging of lithium-ion batteries have largely focused on alleviating through-plane lithiation gradients while little is understood about in-plane heterogeneities and how to resolve them. Herein, high-speed synchrotron X-ray diffraction (XRD) resolves graphite lithiation spatially and temporally during 6 C charging and 2 C discharging. At every point during operation, considerable differences in the state of lithiation across the pouch cell are present. Some regions are more responsive to operation than others, reaching full lithiation early during charge and full delithiation during discharge. Other regions within the cell never fully delithiate during discharge, despite a prolonged voltage hold at 2.8 V. Using time-resolved XRD data, the calculated local current density (mA cm−2) at the graphite surface shows an unexpected occurrence of local inverted current densities where regions of graphite are observed to delithiate during charging and lithiate during discharging. A pseudo-3D model is developed for the graphite electrode with spatially varying microstructural tortuosity to show how microstructural heterogeneity could influence spatial charge dynamics. The model could not predict the complex in-plane charge behavior observed within the cell. Consequently physics-based charging protocols based on homogeneous electrode assumptions may underestimate the local variations in charge dynamics and occurrence of lithium plating.

With this issue, we are opening the third volume of Small Science. For a young journal that aims to establish an eminent reputation in the scientific community, this is an exciting time. Even though we have seen two very successful years at this point, the challenges and demands for a modern and impactful scholarly journal are continuously increasing. For our readers and authors, we strive for the presentation of a publishing platform that adheres to the highest standards of research integrity, reproducibility, and editorial processes. At the same time, your best research deserves a maximum of accessibility and visibility, fairness during editorial evaluation and peer review, as well as speedy processing. This can only be accomplished by a consistent development of our editorial workflows journal. Thus, our team is continuously working on the improvement of technical processes and editorial policies to guarantee highest quality for the manuscripts we publish in alignment with an excellent publishing experience. Below, I would like to illustrate the most important developments within the last year. While our colleague Debora Walker unfortunately left the team in 2022, we welcome two new editors. Jiaqi Li, based in Beijing, China, and Sneha K. Rhode, based in Oxford, UK, ho are already integral parts of Small Science efficiently contributing with their scientific and editorial expertise on a daily basis. More recently, José Olivera had to step down from his role as Editor-in-Chief of Small due to his wider leadership role within Wiley. Neville Compton has now taken over the role as Small's Editor-in-Chief and as Publisher for our nanoscience portfolio including our sister journals Small Methods, Small Structures, and Nano Select. With 30 years of experience in scholarly publishing as well as various leadership roles in Wiley's Chemistry portfolio, Neville is ideally qualified to coordinate our portfolio on a strategic level. To get an impression on our whole Small family, visit our new special collection: Best of the Small journals 2022, where outstanding manuscripts from our journals are showcased. Based on the very positive feedback for our virtual symposium “Spotlights in Small Science” in 2021, we decided to host another event together with our sister journal Advanced Science. We were honored that highly renowned researchers Zhenan Bao (Stanford Uni., USA), Ali Khademhosseini (Terasaki Inst., Los Angeles, USA), and Hua Kuang (Jiangnan Uni., Wuxi, China) presented their results in the session “Advances in Biomedical Research” whereas Shengzhong (Frank) Liu (Chinese Academy of Sciences, Dalian, China), Arumugam Manthiram (Uni. of Texas at Austin, USA), and Stefan Hecht (DWI Leibniz Inst. for Interactive Materials, Germany) talked about their outstanding research in the session “Advances in Smart Materials and Energy Research”. You can access recordings of these exceptionally interesting symposia here. Wiley-VCH editors have developed a new feature to standardize data reporting in collaboration with expert researchers: data reporting checklists. These cover sheets are now a part of our submission process for original research articles. Each checklist indicates what we consider the absolute minimum parameters that should be reported in manuscripts for a particular field of research. Data reporting checklists not only assist authors to understand data reporting expectations and guide their manuscript preparation, but also help reviewers during manuscript evaluation. Currently, we have checklists available for research involving the performance/stability of solar cells or for batteries and supercapacitors; additional checklists for other research areas are under development. In the course of the year, we will start publishing the checklists along with the Supporting Information files for accepted manuscripts. As a reviewer, you may have noticed that we introduced a new workflow in our journals. Small Science and its sister journals now notify our reviewers of the editorial decision for the manuscripts they evaluated. The other, anonymized, reviewer reports are also shared. We believe this new workflow enhances the transparency of our editorial decision-making process and gives our reviewers valuable insight into their peers’ evaluation of the manuscript and additional guidance as to the journal's standards. The feedback we have received indicates our reviewers are appreciative not just of the information provided in the notification but also how it acknowledges the important contribution they make to upholding our stringent requirements. The scholarly landscape, especially in the context of open access publishing, is changing at a fast pace. It can be challenging for scientists to follow new funder mandates or transitional open access agreements that may affect their selection of the right journal. Therefore, we actively support our authors with up-to-date resources such as our Author Compliance Tool and convenient processes like our Author Services Dashboard. We are very grateful, and also proud, to see that researchers choose Small Science as the platform to publish their cutting-edge research. This is not only reflected in high citation numbers but also outstanding access and download numbers for our manuscripts. In Table 1, you will find the current most accessed manuscripts published in our journal. The high quality of our editorial processes and our articles also entailed Small Science to being included in additional important indexing services such as CAS: Chemical Abstracts Service (ACS) and the SciTech Premium Collection (ProQuest). We were delighted by the recent confirmation that Small Science will receive its first Journal Impact Factor (Clarivate) in 2023 as this represents another important milestone for a young journal. Our exceptional Journal Immediacy Index of 4.8 (December 2022) leads to a very positive expectation for our Journal Impact Factor in the coming years. Table 1. Top 10 most accessed and downloaded articles (as of December 2022) Title Authors (* Corresponding) Affiliation Functional Ink Formulation for Printing and Coating of Graphene and Other 2D Materials: Challenges and Solutions Mohammad Jafarpour, Frank Nüesch, Jakob Heier,* Sina Abdolhosseinzadeh* Laboratory for Functional Polymers, Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf, Switzerland Small-Scale Big Science: From Nano- to Atomically Dispersed Catalytic Materials Ligang Wang, Huan Liu, Jiahao Zhuang, Dingsheng Wang* Department of Chemistry, Tsinghua University, Beijing, China Chemical Vapor Deposition of 4 Inch Wafer-Scale Monolayer MoSe 2 Jiawei Li, Shuopei Wang,* Lu Li, Zheng Wei, Qinqin Wang, Huacong Sun, Jinpeng Tian, Yutuo Guo, Jieying Liu, Hua Yu, Na Li, Gen Long, Xuedong Bai, Wei Yang, Rong Yang, Dongxia Shi, Guangyu Zhang* Songshan Lake Materials Laboratory, Dongguan, Guangdong, China; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190 China Electrocatalytic C–N Coupling for Urea Synthesis Chen Chen,* Nihan He, Shuangyin Wang* State Key Laboratory of Chem/Bio-Sensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha, China High-Voltage Electrolyte Chemistry for Lithium Batteries Kanglong Guo, Shihan Qi, Huaping Wang, Junda Huang, Mingguang Wu, Yulu Yang, Xiu Li,* Yurong Ren,* Jianmin Ma* School of Materials and Energy, University of Electronic Science and Technology of China, Chengdu, Sichuan, China Electrohydrodynamic Jet Printing: Introductory Concepts and Considerations Nhlakanipho Mkhize, Harish Bhaskaran* Department of Materials, University of Oxford, Parks Road, Oxford, United Kingdom Two-Dimensional Materials for Integrated Photonics: Recent Advances and Future Challenges Jianghong Wu, Hui Ma, Peng Yin, Yanqi Ge, Yupeng Zhang, Lan Li,* Han Zhang,* Hongtao Lin* Key Lab. of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang, College of Information Science & Electronic Engineering, Zhejiang University, Hangzhou, China β-Mercaptoethanol-Enabled Long-Term Stability and Work Function Tuning of MXene Hongyue Jing, Benzheng Lyu, Yingqi Tang, Sungpyo Baek, Jin-Hong Park, Byoung Hun Lee, Jin Yong Lee, Sungjoo Lee* SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, Korea; Department of Nano Engineering, Sungkyunkwan University, Suwon, Korea Carbon Dots in Bioimaging, Biosensing and Therapeutics: A Comprehensive Review Boyang Wang, Huijuan Cai, Geoffrey I. N. Waterhouse, Xiaoli Qu,* Bai Yang, Siyu Lu* Green Catalysis Center, College of Chemistry, Zhengzhou University, Zhengzhou, China A Novel Strategy in Electromagnetic Wave Absorbing and Shielding Materials Design: Multi-Responsive Field Effect Yue Zhao, Lele Hao, Xindan Zhang, Shujuan Tan,* Haohang Li, Jing Zheng,* Guangbin Ji* College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing, China With our steady efforts to improve the publishing experience and the outreach as well as quality of our manuscripts, we are convinced that Small Science is in a perfect position to flourish further in the years to come. I would like to thank all editorial board members, authors, and reviewers for their ongoing support and their indispensable contributions to this young journal on its successful journey. Small Science is looking forward to continuously providing the best service to our community. We wish you all a happy and healthy year 2023! On behalf of the editorial team, Ulf Scheffler (Editor-in-Chief)

Polymer solid electrolytes (SEs) with high safety and flexibility are ideal for advanced lithium-metal solid-state batteries (SSBs). Among various polymer SEs, polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) polymer SEs have gained increased attention for their high dielectric constants, high ionic conductivity, and excellent flexibility. However, severe side reactions at the interface caused by the decomposition of residual DMF solvent significantly reduce the cycle life of PVDF-HFP-based SSBs. Herein, La2O3 nanoparticles are used as new inorganic fillers to form a PVDF-HFP/LiFSI/La2O3-40% composite polymer electrolyte (PVDF-HFP/La2O3 CPE). Benefiting from the interaction between La2O3 and N,N-dimethylformamide (DMF) solvent molecules, the cell cycling stability is greatly improved. In addition, the PVDF-HFP/LiFSI solid electrolyte (PVDF-HFP SE) containing 40 wt% La2O3 has the highest ionic conductivity of 1.33 × 10−3 S cm−1 at 25 °C. It also exhibits a higher lithium-ion transference number of 0.52 and lower polarization. The PVDF-HFP/La2O3 CPE here ensures high ionic conductivity and stable interface chemistry in SSB, demonstrating a promising application potential.

Low-cost metal oxide sensors are highly attractive for emerging applications such as breath analysis. Particularly promising are p-type sensors that can operate at low temperatures, a key requirement for compact and low-power devices. To date, however, these sensors lack sufficient sensitivity, selectivity, and humidity robustness to fulfil stringent requirements faced in real applications. Herein, a flame-made and low-power sensor (operated at 150 °C) that consists of CeO2-decorated CuO nanoparticles is introduced, as determined by X-ray diffraction and X-ray photoelectron spectroscopy analysis. Most remarkably, this sensor features excellent robustness to 10–90% relative humidity. This is attributed to the presence of CeO2 nanoclusters, which may act by scavenging OH− and allow the readsorption of oxygen onto the CuO surface. To demonstrate its immediate impact, this sensor is investigated for the detection of acetone, a biomarker for fat burning. It detects acetone with high sensitivity (i.e., 50 ppb) and features excellent acetone selectivity (>9.8) toward key inorganic interferants (i.e., NH3, H2, and CO). Most importantly, the CeO2–CuO sensor accurately quantifies acetone concentrations in the exhaled breath of 16 volunteers (bias and precision of 90 and 457 ppb). As a result, it is attractive for low-power and humidity robust detection of volatiles in breath analysis.

Electrochemical surface-enhanced Raman scattering (EC-SERS) is a promising technique for the diagnosis of trace amounts of neurotransmitters, because it can elucidate neurotransmitters’ behavior on electrodes to deduce their functions in the human body. However, the current EC-SERS devices need several tens of milliliters of analyte solution to collect enough signal for analysis. Miniaturization of EC-SERS devices is crucial for the early diagnosis of disease and point-of-care testing. Herein, a new type of EC-SERS sensor based on 3D microfluidic chips for the analysis of neurotransmitters in ultrasmall volumes is proposed. The microfluidic EC-SERS chip is fabricated by a ship-in-a-bottle technique based on hybrid laser processing. The working electrode is modified using silver/zinc oxide materials, enabling the formation of a unique “candy apple” structure. To assess the fabricated microfluidic EC-SERS chips, ascorbic acid is analyzed using the ingenious microfluidic EC-SERS chips to elucidate its redox reaction by EC-SERS spectroscopy. Significantly, a sub-10 μL volume of analyte solution is sufficient for EC-SERS analysis, which is several orders smaller in volume than the requirements of current EC-SERS devices. The unprecedented microfluidic EC-SERS chips fabricated by the ship-in-a-bottle integration technique can be used in portable and smart analyzers for next-generation biomedicines and catalysts.

Metamaterials are artificially designed materials with multilevel-ordered microarchitectures, which exhibit extraordinary properties not occurring in nature, and their applications have been widely exploited in various research fields. However, the progress of metamaterials for biomedical applications is relatively slow, largely due to the limitations in the size tailoring. When reducing the maximum size of metamaterials to nanometer scale, their multilevel-ordered microarchitectures are expected to obtain superior functions beyond conventional nanomaterials with single-level microarchitectures, which will be a prospective candidate for the next-generation diagnostic and/or therapeutic agents. Here, a forward-looking discussion on the superiority of nano-metamaterials for magnetic resonance imaging (MRI) according to the imaging principles, which is attributed to the unique periodic arrangement of internal multilevel structural units in nano-metamaterials, is presented. Moreover, recent advances in the development of nano-metamaterials for high-performance MRI are introduced. Finally, the challenges and future perspectives of nano-metamaterials as promising MRI contrast agents for biomedical applications are briefly commented.