Microfluidic sample preparation for diagnostic cytopathology

Abstract

The cellular components of body fluids are routinely analyzed to identify disease and treatment approaches. While significant focus has been placed on developing cell analysis technologies, tools to automate the preparation of cellular specimens have been more limited, especially for body fluids beyond blood. Preparation steps include separating, concentrating, and exposing cells to reagents. Sample preparation continues to be routinely performed off-chip by technicians, preventing cell-based point-of-care diagnostics, increasing the cost of tests, and reducing the consistency of the final analysis following multiple manually-performed steps. Here, we review the assortment of biofluids for which suspended cells are analyzed, along with their characteristics and diagnostic value. We present an overview of the conventional sample preparation processes for cytological diagnosis. We finally discuss the challenges and opportunities in developing microfluidic devices for the purpose of automating or miniaturizing these processes, with particular emphases on preparing large or small volume samples, working with samples of high cellularity, automating multi-step processes, and obtaining high purity subpopulations of cells. We hope to convey the importance of and help identify new research directions addressing the vast biological and clinical applications in preparing and analyzing the array of available biological fluids. Successfully addressing the challenges described in this review can lead to inexpensive systems to improve diagnostic accuracy while simultaneously reducing overall systemic healthcare costs.

Figure 1

Standard procedure in collecting, preparing and analyzing biofluid samples for cytodiagnostics. Biofluid specimens are collected from the patient and transported to a cytopathology laboratory. Freshly collected samples are prepared with multiple centrifugation and manual handling steps including cell fixing, washing, and cytochemical staining. These are necessary steps for preparing cell-based assays including cell smears, cell blocks and cell solutions. Prepared samples undergo microscopic examination, flow cytometry, and cytogenetic analysis. From the initial collection of biofluid samples until final analysis is complete, the time spent during the sample preparation portion has the longest duration, relative to sample collection and sample analysis.

Figure 2

The human system produces biofluids to complete bodily functions. The constant secretion, absorption, and circulation of fluid in the body and the rich source of cellular material make it a valuable medium for liquid-based cytology. Such liquid-based samples present vast opportunities in bridging medical and clinical applications with microfluidic technologies for sample preparation and analysis.

Figure 3

Sample preparation of biofluids to improve throughput and purity. Macroscale instruments like the centrifuge specialize in throughput while microscale technologies emphasize on purity. Both high throughput and purity are useful alone, but for some samples it will be clinically useful to have technologies that can process fluids at high throughputs and with high purity (e.g. isolating malignant cells from pleural fluids for nucleic acid analysis).