An enzyme-linked immunosorbent assay on a centrifugal platform using magnetic beads

Fully Integrated and High-Throughput Microfluidic System for Multiplexed Point-Of-Care Testing

For every epidemic outbreak, the prevention and treatments in resource-limited areas are always out of reach. Critical to this is that high accuracy, stability, and more comprehensive analytical techniques always rely on expensive and bulky instruments and large laboratories. Here, a fully integrated and high-throughput microfluidic system is proposed for ultra-multiple point-of-care immunoassay, termed Dac system. Specifically, the Dac system only requires a handheld portable device to automatically recycle repetitive multi-step reactions including on-demand liquid releasing, dispensing, metering, collecting, oscillatory mixing, and discharging. The Dac system performs high-precision enzyme-linked immunosorbent assays for up to 17 samples or targets simultaneously on a single chip. Furthermore, reagent consumption is only 2% compared to conventional ELISA, and microbubble-accelerated reactions shorten the assay time by more than half. As a proof of concept, the multiplexed detections are achieved by detecting at least four infection targets for two samples simultaneously on a singular chip. Furthermore, the barcode-based multi-target results can rapidly distinguish between five similar cases, allowing for accurate therapeutic interventions. Compared to bulky clinical instruments, the accuracy of clinical inflammation classification is 92.38% (n = 105), with a quantitative correlation coefficient of R2 = 0.9838, while the clinical specificity is 100% and the sensitivity is 98.93%.

Multiple on-line active valves based centrifugal microfluidics for dynamic solid-phase enrichment and purification of viral nucleic acid

Point of care testing (POCT) of nucleic acids holds significant importance in the realm of infectious disease prevention and control, as well as the advancement of personalized precision medicine. Nevertheless, conventional nucleic acid testing methods continue to face challenges such as prolonged detection times and dependence on extensive specialized equipment and personnel, rendering them unsuitable for point of care applications. Here, we proposed an innovative active centrifugal microfluidic system (ACMS) for automatic nucleic acid extraction, encompassing modules for active valve control and magnetic control. An on-chip centrifugal puncture valve (PV) was devised based on the elastic tolerance differences between silicone membranes and tinfoils to release pre-embedded liquid reagents on demand. Furthermore, we have utilized the returnable valve (RV) technology to accurately control the retention and release of liquids, leveraging the high elastic tolerance of the silicone membrane. By incorporating an online controllable magnetic valve, we have achieved controlled and rapid aggregation and dispersion of magnetic beads. The final chip encapsulates multiple reagents and magnetic beads necessary for nucleic acid extraction. Upon sample addition and loading into the instrument, automated on-chip sample loading and nucleic acid extraction, purification, and collection can be accomplished within 30 minutes, halving the overall operation time and even increasing the efficiency of pseudovirus extraction by three orders of magnitude. Consequently, real-time fluorescence quantitative PCR amplification has successfully detected multiple targets of the SARS-CoV-2 virus (with an impressive detection limit as low as 10 copies per μL), along with targeted sequencing analysis yielding a conformity rate of 99%.

ImmunoDisk—A Fully Automated Bead-Based Immunoassay Cartridge with All Reagents Pre-Stored

In this paper, we present the ImmunoDisk, a fully automated sample-to-answer centrifugal microfluidic cartridge, integrating a heterogeneous, wash-free, magnetic- and fluorescent bead-based immunoassay (bound-free phase detection immunoassay/BFPD-IA). The BFPD-IA allows the implementation of a simple fluidic structure, where the assay incubation, bead separation and detection are performed in the same chamber. The system was characterized using a C-reactive protein (CRP) competitive immunoassay. A parametric investigation on air drying of protein-coupled beads for pre-storage at room temperature is presented. The key parameters were buffer composition, drying temperature and duration. A protocol for drying two different types of protein-coupled beads with the same temperature and duration using different drying buffers is presented. The sample-to-answer workflow was demonstrated measuring CRP in 5 µL of human serum, without prior dilution, utilizing only one incubation step, in 20 min turnaround time, in the clinically relevant concentration range of 15–115 mg/L. A reproducibility assessment over three disk batches revealed an average signal coefficient of variation (CV) of 5.8 ± 1.3%. A CRP certified reference material was used for method verification with a concentration CV of 8.6%. Our results encourage future testing of the CRP-ImmunoDisk in clinical studies and its point-of-care implementation in many diagnostic applications.

Disk-based enzyme-linked immunosorbent assays using the liquid-aliquoting and siphoning-evacuation technique

A cost-effective way to carry out multiple enzyme-linked immunosorbent assays (ELISAs) on a centrifugal platform using the liquid-aliquoting and siphoning-evacuation (LASE) technique was developed in this paper. Instead of preloading all the reagents in the reservoirs before testing, each reagent was loaded only one time during testing. The reagent was distributed into equal aliquots and delivered into reaction chambers by the aliquoting fluidic function. In addition, a siphoning-evacuation technique was developed to improve the washing efficiency and simplify the assay protocol. Furthermore, the entire assay protocol can be conducted using a two-step spinning protocol, which greatly reduces the cost of the motor control system. With the LASE technique, a low-cost and user-friendly ELISA system can be achieved.

Nominal effective immunoreaction volume of magnetic beads at single bead level

Immunomagnetic bead (IMB)-based enzyme-linked immunosorbent assay (ELISA) has been the tool frequently used for protein detection in research and clinical laboratories. For most ELISA reactions the recommended dosage of IMBs is usually according to their weight (mg) or mass fraction (w/v) instead of the bead number. Consequently, the processes occurring in the immediate vicinity of the IMBs have always been ignored by researchers and they cannot be revealed in detail during the ELISA reaction. In this paper, we established the relationship between number of IMBs and colorimetric results, and further proposed a new concept of "nominal effective immunoreaction volume (NEIV)" to characterize a single IMB during ELISA reaction. Results showed that the NEIV of a single IMB has a constant value, which is unrelated to the amount of beads and the concentration of antigen. Optimal results of the colorimetric ELISA are achieved when the incubation volume meets each IMB's NEIV and is no longer enhanced by increasing the incubation volume. Thus, the reliable and relatively precise number of IMBs for ELISA detection during practical application could be determined. Most importantly, a study using IMB's NEIV would lay the foundation for a kinetics analysis of IMBs and antigens for future study.

C-reactive protein and interleukin 6 microfluidic immunoassays with on-chip pre-stored reagents and centrifugo-pneumatic liquid control

We present a fully automated centrifugal microfluidic method for particle based protein immunoassays. Stick-pack technology is employed for pre-storage and release of liquid reagents. Quantitative layout of centrifugo-pneumatic particle handling, including timed valving, switching and pumping is assisted by network simulations. The automation is exclusively controlled by the spinning frequency and does not require any additional means. New centrifugal microfluidic process chains are developed in order to sequentially supply wash buffer based on frequency dependent stick-pack opening and pneumatic pumping to perform two washing steps from one stored wash buffer; pre-store and re-suspend functionalized microparticles on a disk; and switch between the path of the waste fluid and the path of the substrate reaction product with 100% efficiency. The automated immunoassay concept is composed of on demand ligand binding, two washing steps, the substrate reaction, timed separation of the reaction products, and termination of the substrate reaction. We demonstrated separation of particles from three different liquids with particle loss below 4% and residual liquid remaining within particles below 3%. The automated immunoassay concept was demonstrated by means of detecting C-reactive protein (CRP) in the range of 1-81 ng ml^-1 and interleukin 6 (IL-6) in the range of 64-13 500 pg ml^-1. The limit of detection and quantification were 1.0 ng ml^-1 and 2.1 ng ml^-1 for CRP and 64 pg ml^-1 and 205 pg ml^-1 for IL-6, respectively.

Centrifugal multiplexing fixed-volume dispenser on a plastic lab-on-a-disk for parallel biochemical single-end-point assays

In this study, a multiple sample dispenser for precisely metered fixed volumes was successfully designed, fabricated, and fully characterized on a plastic centrifugal lab-on-a-disk (LOD) for parallel biochemical single-end-point assays. The dispenser, namely, a centrifugal multiplexing fixed-volume dispenser (C-MUFID) was designed with microfluidic structures based on the theoretical modeling about a centrifugal circumferential filling flow. The designed LODs were fabricated with a polystyrene substrate through micromachining and they were thermally bonded with a flat substrate. Furthermore, six parallel metering and dispensing assays were conducted at the same fixed-volume (1.27 μl) with a relative variation of ±0.02 μl. Moreover, the samples were metered and dispensed at different sub-volumes. To visualize the metering and dispensing performances, the C-MUFID was integrated with a serpentine micromixer during parallel centrifugal mixing tests. Parallel biochemical single-end-point assays were successfully conducted on the developed LOD using a standard serum with albumin, glucose, and total protein reagents. The developed LOD could be widely applied to various biochemical single-end-point assays which require different volume ratios of the sample and reagent by controlling the design of the C-MUFID. The proposed LOD is feasible for point-of-care diagnostics because of its mass-producible structures, reliable metering/dispensing performance, and parallel biochemical single-end-point assays, which can identify numerous biochemical.