In the molecular diagnosis platform, microfluidic chip technology, through the integration of a microscale fluid manipulation system, automates the entire sample processing process, from pretreatment to detection. Its core approach is to integrate the fundamental operational units of biochemical experiments (such as sample preparation, reaction, separation, and detection) into a micron-scale chip structure. This approach, combined with sophisticated fluid control techniques and intelligent algorithms, creates an efficient and accurate closed-loop system. This technology relies on the fusion of multi-dimensional technologies encompassing materials science, fluid dynamics, micro-nanofabrication, and biosensing, providing a highly sensitive, low-contamination, and portable solution for molecular diagnostics.
In the automated sample processing process, the microfluidic chip first achieves precise sample distribution through a network of microchannels. The micron-scale flow channel system constructed on the chip surface can be designed into a complex network of pathways, which, combined with non-mechanical or mechanical actuation methods such as pressure, electroosmotic flow, or centrifugal force, delivers samples from the storage area to the reaction zone. For example, vacuum-driven technology uses a pre-evacuated polydimethylsiloxane (PDMS) chip to create negative pressure, driving sample flow through blind-end channels and enabling multi-channel parallel distribution. Centrifugal-driven technology, on the other hand, utilizes the centrifugal force generated by rotation to force sample flow unidirectionally through open-end channels, enabling nucleic acid extraction or reagent mixing. This fluid manipulation method eliminates the risk of cross-contamination associated with traditional manual procedures while significantly reducing sample consumption.
Automating sample pretreatment relies on the integrated design of microfluidic chips. In traditional molecular diagnostics, nucleic acid extraction requires manual processing using magnetic beads or silica membranes. However, microfluidic chips immobilize silica particles on microchannel surfaces, forming miniature solid-phase extraction units. As the sample flows in, DNA molecules automatically adsorb to the silica surface. Impurities are then removed by buffer flushing, and nucleic acid elution is achieved by adjusting the ionic strength or pH. This process requires no external intervention, and the microscale effects of the chip enhance the efficiency of molecular interactions, reducing extraction time to just minutes. In addition, some chips also integrate a cell lysis module, which disrupts cells using chemical lysis solutions or physical shear forces (such as ultrasonic microstructures) within microchannels, further streamlining the process.
Automation of the reaction stage is achieved through the synergy between microreactors and temperature control systems. The reaction chambers in microfluidic chips can be designed with nanoscale dimensions, combined with localized heating elements (such as Peltier heaters) or infrared lasers to precisely control the reaction temperature. For example, in PCR amplification, the chip mixes the sample with primers and enzymes through microchannels and then transports them to a temperature-controlled zone for the denaturation, annealing, and extension cycles. Due to the microreactor's small heat capacity, temperature switching speeds can reach several degrees Celsius per second, far exceeding traditional thermal cyclers, reducing amplification time from several hours to less than half an hour. Furthermore, the chip's laminar flow characteristics avoid convection interference in traditional reactions, ensuring reaction uniformity.
Automation of the detection stage relies on the coupling of highly sensitive sensing technologies with the microfluidic structure. Chips can integrate electrochemical sensors, optical detection modules (such as laser-induced fluorescence), or mass spectrometry interfaces for real-time analysis of amplification products. For example, a microfluidic system combining recombinase polymerase amplification (RPA) with a lateral flow test strip delivers the amplified product to the test strip's detection area through microchannels, where an antibody-antigen reaction enables visual readout. This entire process requires no complex instrumentation and achieves single-molecule sensitivity. Furthermore, digital microfluidics, which manipulates droplets through the electrowetting effect, enables parallel detection of multiple targets, further increasing throughput.
The integration of intelligent algorithms empowers microfluidic chips with adaptive control capabilities. By integrating pressure sensors, flow meters, and image recognition modules, the chip monitors fluid conditions, reaction progress, and detection signals in real time, providing feedback to a central control system to adjust parameters. For example, when sample flow fluctuations are detected, the system automatically adjusts the pressure controller output; when the fluorescence signal approaches a threshold, the amplification cycle is terminated prematurely to save time. This closed-loop control model significantly improves diagnostic robustness and is particularly suitable for use in resource-limited settings or where operator skills vary.
In terms of material selection, PDMS has become the mainstream substrate for microfluidic chips due to its excellent biocompatibility, gas permeability, and optical transparency. Its low elastic modulus facilitates the fabrication of complex microstructures via soft lithography and allows for bonding with materials such as glass and silicon to form sealed chambers. Thermoplastic materials such as polymethyl methacrylate (PMMA) can be mass-produced at low cost through hot pressing, driving the portability and widespread adoption of molecular diagnosis platforms. This diverse selection of materials provides flexible technical support for diverse application scenarios, such as clinical testing and rapid on-site testing.
Microfluidic chip technology for automated sample processing in molecular diagnosis platforms is essentially a product of the intersection of multiple disciplines. Through the deep integration of microscale fluid manipulation, integrated reaction units, high-sensitivity detection, and intelligent algorithms, it reshapes the traditional molecular diagnostic process, enabling unmanned operation from "sample in" to "result out." This technology not only improves diagnostic efficiency and accuracy but also promotes the penetration of molecular diagnostics into emerging scenarios such as point-of-care testing (POCT) and home self-testing, laying the technical foundation for the widespread adoption of precision medicine.
