Microplate cell-retaining methodology for high-content analysis of individual non-adherent unanchored cells in a population

Target Confinement in Small Reaction Volumes Using Microfluidic Technologies: A Smart Approach for Single-Entity Detection and Analysis

Over the last decades, the study of cells, nucleic acid molecules, and proteins has evolved from ensemble measurements to so-called single-entity studies. The latter offers huge benefits, not only as biological research tools to examine heterogeneities among individual entities within a population, but also as biosensing tools for medical diagnostics, which can reach the ultimate sensitivity by detecting single targets. Whereas various techniques for single-entity detection have been reported, this review focuses on microfluidic systems that physically confine single targets in small reaction volumes. We categorize these techniques as droplet-, microchamber-, and nanostructure-based and provide an overview of their implementation for studying single cells, nucleic acids, and proteins. We furthermore reflect on the advantages and limitations of these techniques and highlight future opportunities in the field.

Lens-on-lens microstructures

Microlenses with multiple focal lengths play an important role in three-dimensional imaging and the real-time detection of unconfined or fluctuating targets. In this Letter, we present a novel method of fabricating lens-on-lens microstructures (LLMs) using a two-step femtosecond laser wet etching process. A 3×3 LLM array was made with a diameter of 129.0 μm. The fabricated LLM has two focal lengths, 80.4 and 188.7 μm, showing excellent two-level focusing and imaging abilities. Its size and focal length can be controlled by adjusting laser power and etching time. Its surface roughness remains about 61 nm. This simple and efficient method for large-scale production of LLMs has potential applications in diverse optical systems.

Maskless fabrication of concave microlens arrays on silica glasses by a femtosecond-laser-enhanced local wet etching method

A simple and efficient technique for large-area manufacturing of concave microlens arrays (MLAs) on silica glasses with femtosecond (fs)-laser-enhanced chemical wet etching is demonstrated. By means of fs laser in situ irradiations followed by the hydrofluoric acid etching process, large area close-packed rectangular and hexagonal concave MLAs with diameters less than a hundred of micrometers are fabricated within a few hours. The fabricated MLAs exhibit excellent surface quality and uniformity. In contrast to the classic thermal reflow process, the presented technique is a maskless process and allows the flexible control of the size, shape and the packing pattern of the MLAs by adjusting the parameters such as the pulse energy, the number of shots and etching time.

Miniaturization of biological assays -- overview on microwell devices for single-cell analyses

BACKGROUND

Today, cells are commonly analyzed in ensembles, i.e. thousands of cells per sample, yielding results on the average response of the cells. However, cellular heterogeneity implies the importance of studying how individual cells respond, one by one, in order to learn more about drug targeting and cellular behavior.

SCOPE OF REVIEW

This review discusses general aspects on miniaturization of biological assays and in particular summarizes single-cell assays in microwell formats. A range of microwell-based chips are discussed with regard to their well characteristics, cell handling, choice of material etc. along with available detection systems for single-cell studies. History and trends in microsystem technology, various commonly used materials for device fabrication, and conventional methods for single-cell analysis are also discussed, before a closing section with a detailed example from our research in the field.

MAJOR CONCLUSIONS

A range of miniaturized and microwell devices have shown useful for studying individual cells.

GENERAL SIGNIFICANCE

In vitro assays offering low volume sampling and rapid analysis in a high-throughput manner are of great interest in a wide range of single-cell applications. Size compatibility between a cell and micron-sized tools has encouraged the field of micro- and nanotechnologies to move into areas such as life sciences and molecular biology. To test as many compounds as possible against a given amount of patient sample requires miniaturized tools where low volume sampling is sufficient for accurate results and on which a high number of experiments per cm(2) can be performed. This article is part of a Special Issue entitled Nanotechnologies - Emerging Applications in Biomedicine.

A novel permalloy based magnetic single cell micro array

Devices capable of automatically aligning cells onto geometrical arrays are of great interest to biomedical researchers. Such devices can facilitate the study of numerous cells while the cells remain physically separated from one another. In this way, cell arrays reduce cell-to-cell interactions while the cells are all subjected to common stimuli, which allows individual cell behaviour to be revealed. The use of arrays allows for the parallel analysis of single cells, facilitates data logging, and opens the door to the use of automated machine-based single cell analysis techniques. A novel permalloy based magnetic single cell micro array (MSCMA) is presented in this paper. The MSCMA creates an array of magnetic traps by generating magnetic flux density peaks at predefined locations. When using cells labelled with immunomagnetic labels, the cells will interact with the magnetic fields, and can be captured at the magnetic trap sites. Prototypes of the MSCMA have been successfully fabricated and tested using both fixed and live Jurkat cells (10 microm average diameter) that were labelled. The prototypes performed as predicted during experimental trials. The experimental results show that the MSCMA can randomly array up to 136 single cells per square mm. The results also show that the number of single cells captured is a function of the trap site density of the MSCMA design and the cell density in the fluid sample.

Entrapment and measurement of a biologically functionalized microbead with a microwell electrode

A chip with integrated electrophoretic and electrochemical systems was developed to manipulate either an individual microbead or a cell inside a microwell electrode (MWE) for electrochemical measurement. The optimal MWE geometry (30 microm diameter and 25 microm depth) was designed to accommodate the micro particles according to the simulated results. A chip device was sequentially built from a slide patterned with Pt electrodes, an adhesive tape defined with a flow channel (200 microm in width and 25 microm in height), and an indium tin oxide (ITO) cover. The MWE not only generated an active electrophoretic force to trap the particle but also provided a low flow velocity area (LFVA) to stabilize the trapped bead or cell in a continuous flow. Scanning electrochemical microscopy (SECM) theory was employed to explain the electrochemical behaviors of the MWE. An enhanced current was confirmed as the redox recycling effect on the conductive ITO cover. The catalytic reaction of an individual alkaline phosphatase coated microbead (ALP-bead) was electrochemically detected with the MWE after being trapped. The ALP on the trapped ALP-bead catalyzed the hydrolysis of p-aminophenylphosphate (PAPP) to p-aminophenol (PAP), and then a decaying amperogram (+0.3 V vs. Ag/AgCl) due to a tiny PAP quantity around the MWE was observed.

Functional analysis of individual cells and microenvironment of breast cancer-draining lymph nodes

The development of distant metastases is the major cause of death in breast cancer (BC). In many BC cases, metastases are present in patients with no metastasis-positive lymph nodes (LN). Hence, there is a need to improve prognosis by a better prediction of the nodal status and tumor spread. The current study is designed to develop and utilize new functional characteristics of the cells and microenvironment of BC-draining LN, which may help to improve the estimation of LN metastatic involvement. Innovative devices and methodologies were developed for collecting, transferring, and analyzing LN at an individual-cell resolution. Using these devices, a suspension of living cells were prepared from the LN and processed for various assays, including immunophenotypic analysis, activation status, and invasion activity. The functional profile of tumor-activated LN cells showed an increase in the intracellular enzymatic reaction rate, accompanied by a homogeneous distribution of transferrin receptor as well as by a significant increase in matrix metalloproteinase proteolytic activity. Moreover, the proportion of cells exhibiting such a profile was significantly higher in tumor-containing LN than in tumor-free LN. Thus, the live and postfixation features of LN cells and their microenvironment, correlated with the functional status of the LN, may serve to improve their predictive value in breast cancer examination.

Cellular microarrays for use with capillary-driven microfluidics

We present a method for the facile arraying of cells on microstructured substrates which should be suitable for cellular assays in autonomous microfluidic capillary systems (CSs). The CSs, which were designed and microfabricated in Si, have various microfluidic functional elements including reaction chambers wherein cellular arrays are located. Two methods for arraying the cells were explored. In the first method, a hydrophobic alkanethiol was microcontact-printed on the bottom surface of a microfluidic reaction chamber. The subsequent adsorption of protein-repellent alkanethiols around the printed areas and the deposition from solution of fibronectin (FN) on the hydrophobic areas resulted in an adhesive pattern for the attachment of living human breast cancer cells. This method was limited by the formation of cellular clusters, which proved difficult to remove selectively. The second method employed a poly(dimethylsiloxane) elastomer having oval recessed microstructures. The selective coating of the inner walls of the ovals with FN and the blocking of the mesas around the ovals with bovine serum albumin (BSA) permitted single or multiple cells to be arrayed depending on the size of the ovals. The possibility of sealing CSs with cells arrayed on poly(dimethylsiloxane) may provide a versatile platform for high-throughput experimentation down to the single-cell level.