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3 pages, 179 KiB

Open AccessEditorial

Editorial for the Special Issue on MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing

by Stefano Zampolli

Micromachines 2022, 13(6), 896; https://doi.org/10.3390/mi13060896 - 4 Jun 2022

Viewed by 1286

Abstract

The outbreak of the SARS-CoV-2 pandemic has made the general public aware of the breakthrough technologies which were developed in recent years for state-of-the-art biosensing, and terms such as clinical specificity and sensitivity are now widely understood [...] Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

Research

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14 pages, 5035 KiB

Open AccessArticle

Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

by Yu Chen, Shuangshuang Meng, Kaige Wang, Jintao Bai and Wei Zhao

Micromachines 2021, 12(12), 1592; https://doi.org/10.3390/mi12121592 - 20 Dec 2021

Cited by 2 | Viewed by 2224

Abstract

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the [...] Read more.

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection–diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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12 pages, 3908 KiB

Open AccessArticle

Microfluidic Chip with Two-Stage Isothermal Amplification Method for Highly Sensitive Parallel Detection of SARS-CoV-2 and Measles Virus

by Qin Huang, Xiaohui Shan, Ranran Cao, Xiangyu Jin, Xue Lin, Qiurong He, Yulei Zhu, Rongxin Fu, Wenli Du, Wenqi Lv, Ying Xia and Guoliang Huang

Micromachines 2021, 12(12), 1582; https://doi.org/10.3390/mi12121582 - 19 Dec 2021

Cited by 16 | Viewed by 3012

Abstract

A two-stage isothermal amplification method, which consists of a first-stage basic recombinase polymerase amplification (RPA) and a second-stage fluorescence loop-mediated isothermal amplification (LAMP), as well as a microfluidic-chip-based portable system, were developed in this study; these enabled parallel detection of multiplex targets in [...] Read more.

A two-stage isothermal amplification method, which consists of a first-stage basic recombinase polymerase amplification (RPA) and a second-stage fluorescence loop-mediated isothermal amplification (LAMP), as well as a microfluidic-chip-based portable system, were developed in this study; these enabled parallel detection of multiplex targets in real time in around one hour, with high sensitivity and specificity, without cross-contamination. The consumption of the sample and the reagent was 2.1 μL and 10.6 μL per reaction for RPA and LAMP, respectively. The lowest detection limit (LOD) was about 10 copies. The clinical amplification of about 40 nasopharyngeal swab samples, containing 17 SARS-CoV-2 (severe acute respiratory syndrome coronavirus) and 23 measles viruses (MV), were parallel tested by using the microfluidic chip. Both clinical specificity and sensitivity were 100% for MV, and the clinical specificity and sensitivity were 94.12% and 95.83% for SARS-CoV-2, respectively. This two-stage isothermal amplification method based on the microfluidic chip format offers a convenient, clinically parallel molecular diagnostic method, which can identify different nucleic acid samples simultaneously and in a timely manner, and with a low cost of the reaction reagent. It is especially suitable for resource-limited areas and point-of-care testing (POCT). Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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8 pages, 1334 KiB

Open AccessCommunication

Colorimetric Sensing with Gold Nanoparticles on Electrowetting-Based Digital Microfluidics

by Zhen Gu, Jing-Jing Luo, Le-Wei Ding, Bing-Yong Yan, Jia-Le Zhou, Jun-Gang Wang, Hui-Feng Wang and Cong Kong

Micromachines 2021, 12(11), 1423; https://doi.org/10.3390/mi12111423 - 19 Nov 2021

Cited by 9 | Viewed by 2203

Abstract

Digital microfluidic (DMF) has been a unique tool for manipulating micro-droplets with high flexibility and accuracy. To extend the application of DMF for automatic and in-site detection, it is promising to introduce colorimetric sensing based on gold nanoparticles (AuNPs), which have advantages including [...] Read more.

Digital microfluidic (DMF) has been a unique tool for manipulating micro-droplets with high flexibility and accuracy. To extend the application of DMF for automatic and in-site detection, it is promising to introduce colorimetric sensing based on gold nanoparticles (AuNPs), which have advantages including high sensitivity, label-free, biocompatibility, and easy surface modification. However, there is still a lack of studies for investigating the movement and stability of AuNPs for in-site detection on the electrowetting-based digital microfluidics. Herein, to demonstrate the ability of DMF for colorimetric sensing with AuNPs, we investigated the electrowetting property of the AuNPs droplets on the hydrophobic interface of the DMF chip and examined the stability of the AuNPs on DMF as well as the influence of evaporation to the colorimetric sensing. As a result, we found that the electrowetting of AuNPs fits to a modified Young–Lippmann equation, which suggests that a higher voltage is required to actuate AuNPs droplets compared with actuating water droplets. Moreover, the stability of AuNPs was maintained during the processing of electrowetting. We also proved that the evaporation of droplets has a limited influence on the detections that last several minutes. Finally, a model experiment for the detection of Hg²⁺ was carried out with similar results to the detections in bulk solution. The proposed method can be further extended to a wide range of AuNPs-based detection for label-free, automatic, and low-cost detection of small molecules, biomarkers, and metal ions. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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8 pages, 1790 KiB

Open AccessArticle

A Sensitivity-Enhanced Electrolyte-Gated Graphene Field-Effect Transistor Biosensor by Acoustic Tweezers

by Yan Chen, Wenpeng Liu, Hao Zhang, Daihua Zhang and Xiaoliang Guo

Micromachines 2021, 12(10), 1238; https://doi.org/10.3390/mi12101238 - 13 Oct 2021

Cited by 1 | Viewed by 1803

Abstract

Low-abundance biomolecule detection is very crucial in many biological and medical applications. In this paper, we present a novel electrolyte-gated graphene field-effect transistor (EGFET) biosensor consisting of acoustic tweezers to increase the sensitivity. The acoustic tweezers are based on a high-frequency bulk acoustic [...] Read more.

Low-abundance biomolecule detection is very crucial in many biological and medical applications. In this paper, we present a novel electrolyte-gated graphene field-effect transistor (EGFET) biosensor consisting of acoustic tweezers to increase the sensitivity. The acoustic tweezers are based on a high-frequency bulk acoustic resonator with thousands of MHz, which has excellent ability to concentrate nanoparticles. The operating principle of the acoustic tweezers to concentrate biomolecules is analyzed and verified by experiments. After the actuation of acoustic tweezers for 10 min, the IgG molecules are accumulated onto the graphene. The sensitivities of the EGFET biosensor with accumulation and without accumulation are compared. As a result, the sensitivity of the graphene-based biosensor is remarkably increased using SMR as the biomolecule concentrator. Since the device has advantages such as miniaturized size, low reagent consumption, high sensitivity, and rapid detection, we expect it to be readily applied to many biological and medical applications. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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16 pages, 5293 KiB

Open AccessArticle

Identifying Candidate Biomarkers of Ionizing Radiation in Human Pulmonary Microvascular Lumens Using Microfluidics—A Pilot Study

by Larry J. Millet, Richard J. Giannone, Michael S. Greenwood, Carmen M. Foster, Kathleen M. O’Neil, Alexander D. Braatz and Sandra M. Davern

Micromachines 2021, 12(8), 904; https://doi.org/10.3390/mi12080904 - 29 Jul 2021

Cited by 2 | Viewed by 2043

Abstract

The microvasculature system is critical for the delivery and removal of key nutrients and waste products and is significantly damaged by ionizing radiation. Single-cell capillaries and microvasculature structures are the primary cause of circulatory dysfunction, one that results in morbidities leading to progressive [...] Read more.

The microvasculature system is critical for the delivery and removal of key nutrients and waste products and is significantly damaged by ionizing radiation. Single-cell capillaries and microvasculature structures are the primary cause of circulatory dysfunction, one that results in morbidities leading to progressive tissue and organ failure and premature death. Identifying tissue-specific biomarkers that are predictive of the extent of tissue and organ damage will aid in developing medical countermeasures for treating individuals exposed to ionizing radiation. In this pilot study, we developed and tested a 17 µL human-derived microvascular microfluidic lumen for identifying candidate biomarkers of ionizing radiation exposure. Through mass-spectrometry-based proteomics, we detected 35 proteins that may be candidate early biomarkers of ionizing radiation exposure. This pilot study demonstrates the feasibility of using humanized microfluidic and organ-on-a-chip systems for biomarker discovery studies. A more elaborate study of sufficient statistical power is needed to identify candidate biomarkers and test medical countermeasures of ionizing radiation. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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18 pages, 3116 KiB

Open AccessArticle

Experimental Validation of a Novel Generator of Gas Mixtures Based on Axial Gas Pulses Coupled to a Micromixer

by Florian Noël, Claire Trocquet, Christophe A. Serra and Stéphane Le Calvé

Micromachines 2021, 12(6), 715; https://doi.org/10.3390/mi12060715 - 18 Jun 2021

Cited by 2 | Viewed by 1933

Abstract

In this work, a novel generator of gas mixtures previously numerically investigated and based on axial gas pulses coupled to a micromixer has been conceived, manufactured, and validated. Standard gaseous pollutant mixtures and pure nitrogen or pure air were introduced in a microdevice [...] Read more.

In this work, a novel generator of gas mixtures previously numerically investigated and based on axial gas pulses coupled to a micromixer has been conceived, manufactured, and validated. Standard gaseous pollutant mixtures and pure nitrogen or pure air were introduced in a microdevice designed to generate alternating axial gas pulses which were downstream homogenized by means of a multi-stage modular micromixer. The dilution, and therefore the final pollutant concentration, was controlled by two parameters: the ratio between the times of each of the two gas pulses and the partial pressure of the pollutant(s) mixture added to the device. The gas mixture generator was coupled to an analyzer to monitor the concentration of aromatic pollutants. The response time was optimized to be lower than 2 min in accordance with the analytical instrument. The quantity of pollutants measured at the micromixer’s outlet increased linearly with the expected gas concentration of 3.7–100 ppb generated by this novel microfluidic generator and fitted perfectly with those obtained by a reference gas dilution bench. At 5 ppb, the precision on the concentration generated is close to that obtained with the conventional gas mixing bench, i.e., around 10%. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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13 pages, 2181 KiB

Open AccessArticle

A Low Spring Constant Piezoresistive Microcantilever for Biological Reagent Detection

by Yuan Tian, Rui Zhao, Yi Liu and Xiaomei Yu

Micromachines 2020, 11(11), 1001; https://doi.org/10.3390/mi11111001 - 12 Nov 2020

Cited by 9 | Viewed by 2234

Abstract

This paper introduces a piezoresistive microcantilever with a low spring constant. The microcantilever was fabricated with titanium (Ti) as the piezoresistor, a low spring constant polyimide (PI) layer, and a thin silicon oxide (SiO₂) layer as the top and bottom passive [...] Read more.

This paper introduces a piezoresistive microcantilever with a low spring constant. The microcantilever was fabricated with titanium (Ti) as the piezoresistor, a low spring constant polyimide (PI) layer, and a thin silicon oxide (SiO₂) layer as the top and bottom passive layers, respectively. Excellent mechanical performances with the spring constant of 0.02128 N/m and the deflection sensitivity

(∆ V / V) / ∆ z

of 1.03 × 10⁻⁷ nm⁻¹ were obtained. The output voltage fluctuation of a Wheatstone bridge, which consists of four piezoresistive microcantilevers, is less than 3 μV@3 V in a phosphate buffered saline (PBS) environment. A microcantilever aptasensor was then developed through functionalizing the microcantilevers with a ricin aptamer probe, and detections on ricin with concentrations of 10, 20, 50 and 100 ng/mL were successfully realized. A good specificity was also confirmed by using bovine serum albumin (BSA) as a blank control. The experiment results show that the Ti and PI-based microcantilever has great prospects for ultrasensitive biochemical molecule detections with high reliability and specificity. Full article

(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)

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