Small Volume Of Liquid Research Articles

Transport Properties of Protic Ionic Liquids Based on Triazolium and Imidazolium: Development of an Air-Free Conductivity Setup.

The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C2HTr124]) and the ethylimidazolium ([C2HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients were measured and discussed, extending the discussion to the concept of fragility. Furthermore, in order to allow the measurement of the ionic conductivity of very small volumes (<0.5 mL) of ionic liquid under an inert and dry atmosphere, a new setup was developed. It was found that the cation nature strongly affected the transport properties, the [C2HTr124] cation resulting in slower dynamics than the [C2HIm] one. This was concluded from both conductivity and diffusivity measurements while for both properties, the anion had a lesser effect. By fitting the conductivity data with the Vogel-Fulcher-Tammann (VFT) equation, we could also estimate the fragility of these ionic liquids, which all fell in the range of very fragile glass-forming materials. Finally, the slower dynamics observed in the triazolium-based ionic liquids can be rationalized by the stronger interactions that this cation establishes with both anions, as deduced from the frequency analysis of relevant Raman signatures and density functional theory (DFT) calculations.

Rupture distances and capillary forces of liquid bridges: Closed-form expressions and ANNs-trained prediction models

Accurate prediction of rupture distances and capillary forces of liquid bridges is crucial for studying the behaviour of wet granular materials. However, the validity of existing analytical expressions is limited to small liquid volumes, whereas current closed-form expressions require numerous calibrated coefficients, making them cumbersome. To overcome these limitations, this study employs Particle Swarm Optimization (PSO), a metaheuristic algorithm, to enhance closed-form expressions. This approach allows tuning the balance between accuracy and complexity, resulting in simplified yet accurate closed-form expressions for liquid bridges with varying volumes and contact angles between unequal-sized particles, under both volume and suction control conditions.Additionally, Artificial Neural Networks (ANNs) are used as an alternative approach. All network architectures up to three hidden layers are systematically explored, and prediction models for rupture distances and capillary forces of liquid bridges are trained using a database of numerical solutions of the Young–Laplace equation. The resulting models provide accurate predictions across a wide range of liquid volumes and contact angles.

Hierarchical ‘rose-petal’ ZnO/Si surfaces with reversible wettability reaching complete water repellence without chemical modification

Smart surfaces with externally controlled wettability patterns are ubiquitous building blocks for micro-/nanofluidic and lab-on-chip devices, among others. We develop hierarchical surfaces of ZnO nanorods grown on laser-microstructured silicon with reversible photo-induced and heat-induced wettability. The as-prepared surfaces are superhydrophilic, with very low water contact angles (~ 10°), and transition to a wetting state with high water contact angles (~ 150°) when annealed in vacuum. As the annealing temperature increases to 400 °C, the surfaces become completely water-repellent. Even though the annealed surfaces present high water contact angles, at the same time, they are very adhesive for water droplets, which do not roll off even when tilted at 90° or 180o (rose-petal effect), unlike standard hydrophobic surfaces which typically combine high water contact angles with low roll-off angles. The surfaces return to the superhydrophilic state when irradiated with UV light, which indicates a reversible wettability with external stimuli. Based on this transition, we demonstrate local modification of the wetting state of the surfaces by UV irradiation through a mask, which results in directed liquid motion, useful for microfluidic applications. The high contact angles obtained in this work are usually obtained only after chemical modification of the ZnO surface with organic coatings, which was not necessary for the hierarchical surfaces developed here, reducing the cost and processing steps of the fabrication route. These rose-petal surfaces can be used as “mechanical hands” in several applications, such as no-loss transport of small liquid volumes, precision coatings, spectroscopy, and others. Furthermore, the completely water-repellent surfaces, rarely reported elsewhere, may find important applications in frictionless liquid transport for microfluidic and other devices.

Spatial distribution of the quantized vortices' tangle in thermally driven round jets of superfluid helium

Thermally driven flows of superfluid 4He display unique features, often related to the presence of quantized vortices—line singularities embedded in the liquid. Here, we focus on turbulent round jets, experimentally investigated using the flow visualization and second sound attenuation techniques, at Reynolds numbers exceeding 104. These turbulent flows are driven by releasing heat into a small volume of liquid, open to the surrounding bath through a cylindrical nozzle, 2 mm in diameter. Our measurements reveal in unprecedented detail how the tangle of quantized vortices associated with the jets arranges itself in space, for distances ranging from 9 to 34 nozzle diameters, at fluid temperatures between 1.64 and 2.10 K. We specifically find that the vortex tangle spreads in the radial direction, while it dilutes away from the nozzle. Additionally, the tangle density is found to systematically depend on the flow forcing. Two physical interpretations of the observed behavior are proposed, which could motivate further investigations of this peculiar flow. One leads us to conjecture a self-similar functional form of the vortex tangle density across counterflow jets. The other suggests that the position of the superfluid stagnation point—a characteristic feature of counterflow jets—could depend on the flow forcing as well.

Responsive materials and mechanisms as thermal safety systems for skin-interfaced electronic devices

Soft, wireless physiological sensors that gently adhere to the skin are capable of continuous clinical-grade health monitoring in hospital and/or home settings, of particular value to critically ill infants and other vulnerable patients, but they present risks for injury upon thermal failure. This paper introduces an active materials approach that automatically minimizes such risks, to complement traditional schemes that rely on integrated sensors and electronic control circuits. The strategy exploits thin, flexible bladders that contain small volumes of liquid with boiling points a few degrees above body temperature. When the heat exceeds the safe range, vaporization rapidly forms highly effective, thermally insulating structures and delaminates the device from the skin, thereby eliminating any danger to the skin. Experimental and computational thermomechanical studies and demonstrations in a skin-interfaced mechano-acoustic sensor illustrate the effectiveness of this simple thermal safety system and suggest its applicability to nearly any class of skin-integrated device technology.

Broadband cavity enhanced UV-VIS absorption spectroscopy for picolitre liquid samples.

Absorption spectroscopy is a widely used analytical technique due to its label-free nature, however its application to small liquid samples is hampered by the associated short absorption pathlengths, which limit sensitivity. A novel concept for the development of an ultrasensitive broadband absorption spectrometer optimised for thin liquid films is presented here. To enhance sensitivity of the absorbance measurements an optical cavity is implemented on a fibre-based absorption spectrometer (CEASpec). Light is circulated multiple times through the sample of interest to increase sensitivity. The bandwidth of the instrument is chosen by the choice of the dielectric mirrors forming the optical cavity spectra and, in this implementation, has been set to be 200 nm wide (250-450 nm). The sensing volume of the spectroscope is prescribed by the choice of optical fibres employed to deliver light to the sample, and in this implementation fibres of 400 μm in diameter were employed, giving a sensing volume of 630 picolitres for a thin film of 5 μm in thickness. Amphotericin B, a broad light absorber in the 280-450 nm region of the spectrum, was used here to prove the capabilities of the proposed cavity enhanced absorption spectroscope. Cavity enhancement factors, the equivalent pathlength increase over classical absorption spectroscopy, in the range of 200× have been achieved across a broad wavelength range.

О стабильности капель катализатора на границе контакта пар-жидкость-кристалл в процессе роста нитевидных нанокристаллов

The paper provides a physical justification for the wettability conditions for a crystalline surface of a limited area by a small-volume catalytic liquid at the end of a growing nanowires (NW) characterized by a contact angle β, which contributes to a fundamental understanding of the nature of the contact angle of catalyst drops at the top of the NW. It is shown that under the conditions of stationary growth of NWs with a transverse singular face, there are only values of the angles β and γ (the angle of inclination of the side surface of the crystal to this face), which correspond to the minimum increment of the free energy of the three-phase system αLVcosβ + αSL = αSVcosγ and determine the stability of the catalyst drop at the top of the NW. With the growth of cylindrical NWs, the conditions of indifferent equilibrium are realized at the drop wetting perimeter. A drop, due to the dissolution of a crystallizing substance or its separation from a liquid solution, can take an equilibrium shape with a contact angle β that does not satisfy the equilibrium contact angle condition θ in the Young equation. A concentric break (rib) at the NW tip should increase the observed wetting angle θ and lead to contact angle hysteresis. The restrictions imposed on the value of the contact angle of a stable catalyst drop at the top of the NW are determined. The catalyst drop will take an equilibrium shape if the hysteresis angle β is in the range θ &lt; β ≤ θ' + γ (θ' is the wetting angle of the NW side walls). For the growth of semiconductor NWs in the form of a straight cylinder, γ = 90° and therefore always β &gt; 90°. It is shown that the direction of displacement of the three-phase line relative to the droplet surface is determined by the growth angle φ0: for the nonwetting growth mode of NWs (with a transverse face) φ0 = β – γ; for the wetting growth mode (with the end surface curved near the three-phase line)

Coherent propagation of vortex rings at extremely high Reynolds numbers

We take advantage of the extremely small kinematic viscosity of superfluid $^4$ He to investigate the propagation of macroscopic vortex rings at Reynolds numbers between $2 \times 10^4$ and $4 \times 10^6$ . These inhomogeneous flow structures are thermally generated by releasing short power pulses into a small volume of liquid, open to the surrounding bath through a vertical tube $2$ mm in diameter. We study specifically the ring behaviour between $1.30$ and $1.80$ K using the flow visualization and second sound attenuation techniques. From the obtained data sets, containing more than $2600$ realizations, we find that the rings remain well-defined in space and time for distances up to at least $40$ tube diameters, and that their circulation depends significantly on the travelled distance, in a way similar to that observed for turbulent vortex rings propagating in Newtonian fluids. Additionally, the ring velocity and circulation appear to be influenced solely by a single, experimentally accessible parameter, combining the liquid temperature with the magnitude and duration of the power pulse. Overall, our results support the view that macroscopic vortex rings moving in superfluid $^4$ He closely resemble their Newtonian analogues, at least in the absence of significant thermal effects and at sufficiently large flow scales.

Viscosity Sensors Based on III-Nitride Optical Devices Integrated With Droplet Sliding Channels

In this letter, we demonstrate a miniature viscosity sensor based on GaN-on-sapphire optical device integrated with an inclined flow channel. The monolithic device, consisting of a pair of GaN diodes responsible for light emission and detection, can monitor droplet sliding. Without the need for external optical components, the proposed elegant design of a few centimeters in size is capable of distinguishing the liquid viscosities from 2 to 600 mPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{s}$ </tex-math></inline-formula> in tens of seconds. The proposed optical sensor exhibits attractive features, such as compactness, low cost, ease of operation, and small liquid volume required, making it suitable for practical applications in liquid viscosity measurement.

A novel terahertz integrated sensor for liquid samples detections based on metamaterial and embedded microfluidic channels

THz metamaterial (MM) microfluidic sensors, which can be utilized for the detection of small volume liquid specimen, have attracted much attention in biosensing applications. In this paper, we propose a novel microfluidic channel embedded terahertz MM sensor, which employs split ring resonators (SRRs) and asymmetric two-gap SRRs for the detection of liquid samples. Unlike currently reported THz MM microfluidic sensors utilizing microfluidic superstrate-metal-substrate structure, our approach combines the microfluidic superstrate with substrate, by designing micro-channels underneath the gap of the SRRs within the polydimethylsiloxane substrate. It could be easily fabricated by standard photolithography techniques. The simulated results show that the performance of the sensor is dependent on the spacing angle between two gaps, the orientation of the gaps, as well as the polarization of electric fields. Furthermore, maximum Q factors of 9.5 and 44 are achieved for dipole resonance, with corresponding figure of merits of 0.63 and 2.89 RIU−1 for transmission and reflection scenarios. Thus, this concept and method not only provides sensitive biosensing for liquid-based samples, but also can be applied to other MM structures to further improve the sensitivity.

An Improved Split-Ring Resonator-Based Sensor for Microfluidic Applications.

This study proposes an ultrahigh-sensitivity split-ring resonator-based microwave sensor for retrieving the complex permittivity of liquid samples. An interdigital capacitor structure was used to expand the sensing area and the sensitivity. A defected ground structure and A parallel dual split-ring resonator were introduced to improve the quality factor. A polydimethylsiloxane microfluidic channel substrate was placed above the interdigital capacitor structure. The channel route coincided with the interdigital gap to fully utilize the strong electric field. Ethanol-water solutions with varying ethanol fractions were injected into the channel as the testing liquid. It was demonstrated that the variation in resonant frequency can be used to retrieve the dielectric properties of liquid samples. The proposed sensor used a small liquid volume of ~0.68 μL and provided values in good agreement with the reference data.

Energy Dissipation Rate and Micromixing in a Two-Step Micro-Reactor with Intensively Swirled Flows.

The influence of the hydrodynamics (flow rates Q, specific energy dissipation rate ε) on the micromixing in a two-step microreactor with intensively swirled flows (MRISF-2) was studied experimentally. Three methods of liquid input into the reactor were compared: (i) through the upper tangential and axial nozzles (TU1, Ax); (ii) through two upper tangential nozzles (TU1, TU2); (iii) through the upper and lower tangential nozzles (TU1, TL2). Segregation index Xs used as a measure of micromixing level was determined by means of iodide iodate reaction method. The Bernoulli equation for a device with two inputs and one output was derived to assess the energy consumption. It was revealed that in MRISF-2 up to 99.8-99.9% of input energy is dissipated, i.e., transformed into liquid element deformations thus resulting in better micromixing. For each of three liquid inputs, the dependence ε = f(Q) could be fairly approximated by an exponent ε = A1Qn1, with n1 ≈ 3.0. For connection (TU1, TU2) the dependence Xs = f(ε) falls linearly for Q &gt; 2 L/min, but for the low flow rates (Q ≈ 1 L/min) there is an unusually small Xs value; the effect of good micromixing is caused by the kinetic energy concentrated in a small volume of liquid near the neck. The best behavior in terms of micromixing was achieved for the (TU1, Ax) connection scheme: the level of Xs ≈ 0.01 for ε ≈ 30 W/kg, and comes down with growing ε to Xs ≈ 0.002 for ε ≈ 30,000 W/kg. These values are 50 and 250 times lower compared to the mixing in a lab glass with a magnetic stirrer, as shown in our previous work. The parameters of dependencies Xs=A3εn3 were found for (TU1, Ax) and (TU1, TL2).

Utilization of Acoustic Levitation to Calculate the Heat of Polymerization

Heat of polymerization is one important parameter in understanding how chemical additives impact polymerization, especially in additive manufacturing. The well-known equation for heat of polymerization is DH = m*Cp*DT, where m is the mass of the sample, Cp is the pressure constant heat capacity most commonly determined by differential scanning calorimetry (DSC), whilst the change in temperature during polymerization is DT. Normally, thermocouples are utilized to determine the change in temperature during polymerization, however, thermocouples may be affected by thermal interference from their surroundings: the monomers being held within an insulating scintillation vial or similar container.1 Infrared cameras are commonly used, however, the mixture is held between glass plates, once again, generating interference from the surroundings.1 Here we describe a novel technique that eliminates the need for an insulating sample container by using a standing acoustic wave to trap the monomers undergoing polymerization, during which, the change in temperature is recorded by IR thermography.In acoustic levitation, the acoustic standing wave, , is generated utilizing 36 transducers arranged into the two parallel arrays of 3D printed apparatus which emit sound at 40 kHz2. These transducers emit sound waves that interact through constructive and destructive interference to produce nodes able to hold a small volume of liquid in place. This configuration was modified to support two 405 nm lasers on the top and bottom to induce photopolymerization and a FLIR camera was placed to one side (Figure 1). In the experiment, about 5 µL of methyl methacrylate monomer resin containing a photoinitator was placed in a node of the standing wave and the two 405 nm lasers were energized to induce polymerization. A FLIR thermographic camera was used to determine the temperature of the bead throughout the polymerization process. The resulting technique allows for very little thermal interference from the surroundings.The temperature of polymerization measured via our technique ranges from 94.7 to 95.6 °C, very similar to the literature polymerization temperatures of poly(methyl methacrylate) which range from 90 to 94.4 °C.1,3,4 The heat capacities determined from DSC from the beads polymerized via acoustic levitation in this work are from 1.041 to 1.383 J/mol*K, again very near the literature values for neat poly(methyl methacrylate) of 1.117 to 1.38 J/mol*K.5–8 In the end, this technique produces values of DT, and therefore, DH within the literature range without the need for the extended experiments to determine the heat transfer effects of the surrounding vessel.(1) Suzuki, Y.; Cousins, D.; Wassgren, J.; Kappes, B. B.; Dorgan, J.; Stebner, A. P.. Compos. Part Appl. Sci. Manuf. 2018, 104, 60–67. https://doi.org/10.1016/j.compositesa.2017.10.022.(2) UpnaLab. Acoustic Levitator https://www.instructables.com/Acoustic-Levitator/ (accessed 2022 -04 -25).(3) Poly(methyl methacrylate) | Designerdata https://designerdata.nl/materials/plastics/thermo-plastics/poly(methyl-methacrylate) (accessed 2022 -04 -24).(4) Jonathan, P.; Lai, C.-S.; CHEN, C.; 2015. https://doi.org/10.13140/RG.2.2.12658.20165.(5) Melia, T. P. Polymer 1962, 3, 317–319.(6) Pavlinov, L. I.; Rabinovich, I. B.; Okladnov, N. A.; Arzhakov, S. A. Polym. Sci. USSR 1967, 9 (3), 539–544. https://doi.org/10.1016/0032-3950(67)90072-X.(7) Rabinovich, I. B.; Lebedev, B. V.; Melent’eva, T. I. Polym. Sci. USSR 1967, 9 (8), 1913–1921. https://doi.org/10.1016/0032-3950(67)90440-6.(8) Dole, M. Calorimetric Studies of States and Transitions in Solid High Polymers. In Fortschritte Der Hochpolymeren-Forschung; Springer, 1960; pp 221–274. Figure 1

Facile nanoplastics formation from macro and microplastics in aqueous media

The immense production of plastic polymers combined with their discordancy with nature has led to vast plastic waste contamination across the geosphere, from the oceans to freshwater reservoirs, wetlands, remote snowpacks, sediments, air and multiple other environments. These environmental pollutants include microplastics (MP), typically defined as small and fragmented plastics less than 5 mm in size, and nanoplastics (NP), particles smaller than a micrometer. The formation of micro and nanoplastics in aqueous media to date has been largely attributed to fragmentation of plastics by natural (i.e., abrasion, photolysis, biotic) or industrial processes. We present a novel method to create small microplastics (≲ 5 μm) and nanoplastics in water from a wide variety of plastic materials using a small volume of a solubilizer liquid, such as n-dodecane, in combination with vigorous mixing. When the suspensions or solutions are subjected to ultrasonic mixing, the particle sizes decrease. Small micro- and nanoparticles were made from commercial, real world and waste (aged) polyethylene, polystyrene, polycarbonate and polyethylene terephthalate, in addition to other plastic materials and were analyzed using dark field microscopy, Raman spectroscopy and particle size measurements. The presented method provides a new and simple way to create specific size distributions of micro- and nanoparticles, which will enable expanded research on these plastic particles in water, especially those made from real world and aged plastics. The ease of NP and small MP formation upon initial mixing simulates real world environments, thereby providing further insight into the behavior of plastics in natural settings.

Time-Averaged And Time-Resolved Laser Optical Temperature Measurements In Water With Filtered Brillouin Scattering Combined With LDV

A laser measuring system was developed and built that allows to optically measure temperature in water using the method of Filtered Brillouin Scattering (FBS). First time-resolved optical temperature measurements were demonstrated. Furthermore, the FBS-system was combined with an LDV to enable simultaneous measurement of flow velocity and therefore the system is also capable to measure the heat flow. Time-averaged temperature values were determined with good accuracy and, as a special highlight, also time-resolved temperature measurements have been demonstrated with temporal resolution in the order of approximately 10 ms, validated by comparison with fast thermocouple measurements. The overarching goal of the research project was to prepare the market introduction of a laser-optical measuring system for spatially point-based and time-resolved measurement of the heat flow in liquids, especially in water. In order to realize this, it was necessary to measure the local velocity and the local temperature in a liquid. The optical measurement of the local velocity has long been possible using the established method of laser Doppler velocimetry (LDV). Therefore, the heat flow measurement method to be developed should be based on this technology. Until now, there was no suitable optical method for measuring the temperature. In recent years, however, the physical phenomenon of Brillouin scattering has become one focus of measurement technology development. If a small volume of liquid is irradiated with light, the molecules in the liquid scatter back part of the light, which is known as Brillouin scattering. The spectrum of the scattered light depends on the local temperature in the liquid; and it turns out that this physical relationship can be exploited to develop a highly accurate, fast, and non-contact method for measuring temperature. In this paper, we explain the Filtered Brillouin Scattering (FBS) method, show a setup for measuring temperature and velocity in water flows and thus a method for determining the heat flow, and demonstrate the measurement accuracy using a calibration test bench. The temperature measurement accuracy achieved is in the order of 1 K.

Single Whispering-Gallery-Mode Resonator With Microfluidic Chip as a Basis for Multifrequency Microwave Permittivity Measurement of Liquids

The accurate measurement of complex liquid permittivity in a frequency range provides important information on liquid properties in comparison to single frequency permittivity investigations. The multifrequency microwave characterization technique based on a single quartz whispering-gallery-mode (WGM) resonator with a microfluidic chip are proposed, developed, and demonstrated. This technique allows the complex permittivity of small volumes of liquid to be measured at six resonant frequencies in the 30-40 GHz frequency range. The calibration is performed by simulating the measurement cell and by plotting the calibration nomogram charts for all six investigated frequencies. The novel approach is applied in studies of the complex permittivity of the L-lysine in water solutions. The results open up possibilities to investigate the complex permittivity of biological liquids at several frequencies and to further develop the microwave dielectrometry of small liquid volumes in a certain frequency range using the quasi-optical nature of a single high-Q WGM resonator.

Marangoni spreading and contracting three-component droplets on completely wetting surfaces

SignificanceThe shape and dynamics of small sessile droplets are dictated by capillary forces. For liquid mixtures, evaporation adds spatio-temporal modulation to these forces that can either enhance or inhibit droplet spreading, depending on the direction of the resulting Marangoni flow. This work experimentally and numerically demonstrates the coexistence of two antagonistic Marangoni flows in a ternary mixture. Played against each other, they can choreograph a boomerang-like wetting motion: Droplets initially rapidly spread, then contract into a compact cap shape. While such a behavior has been impossible in wetting scenarios of simple liquids, it enables spread-retract-remove surface processing with the addition of a single small liquid volume, demonstrated here in a surface-cleaning experiment.

The impact of microfluidics in high-throughput drug-screening applications.

Drug discovery is an expensive and lengthy process. Among the different phases, drug discovery and preclinical trials play an important role as only 5–10 of all drugs that begin preclinical tests proceed to clinical trials. Indeed, current high-throughput screening technologies are very expensive, as they are unable to dispense small liquid volumes in an accurate and quick way. Moreover, despite being simple and fast, drug screening assays are usually performed under static conditions, thus failing to recapitulate tissue-specific architecture and biomechanical cues present in vivo even in the case of 3D models. On the contrary, microfluidics might offer a more rapid and cost-effective alternative. Although considered incompatible with high-throughput systems for years, technological advancements have demonstrated how this gap is rapidly reducing. In this Review, we want to further outline the role of microfluidics in high-throughput drug screening applications by looking at the multiple strategies for cell seeding, compartmentalization, continuous flow, stimuli administration (e.g., drug gradients or shear stresses), and single-cell analyses.

Extraction and analysis of nicotine (3-(1-methyl-2-pyrrolidinyl)pyridine) from cigarettes using small volume liquid extraction and ultrasonic bath system technique

The tobacco (Nicotiana tabacum) plant belongs to solanaceae family. It is an annual herbaceous plant. Over 0.45 million hectares of land are used for growing tobacco commercially, with a total production of over 750 million kg of tobacco. According to the Global adult tobacco survey held in the year 2016-2017, there are nearly 267 million adults (above 15 years of age) in India abusing tobacco. Nicotine can be extracted from biological samples by liquid-liquid extraction, small volume liquid extraction, etc. Thin-layer chromatography is a very effective technique as it can be employed for many samples simultaneously, which is cost-effective and easy to perform without any errors. A new technique, the Ultrasonic bath technique (Sonication technique) is used for the same. Four different types of solvents were used for extraction purposes out of which two gave favorable results. This methodology is proven to be cost-effective, consumes fewer chemicals, less manpower, and is effective.

Applications of nanopipettes in electrochemical analysis

AbstractNowadays, the application of glass nanopipettes in electrochemical analysis has attracted a lot of attention with the increasing demand for sensitive analysis and diagnostic tools for cellular biomolecules. The ultrasmall nanopipettes are becoming a bridge between the macro‐ and nanoworlds as they can transport very small volumes of liquids and materials as well as acting as electrochemical biosensors. In this minireview, we discuss the fabrication and characterization of nanopipettes and introduce our recent studies using nanopipettes for cell electroanalysis. The future application of nanopipettes has also been discussed.