Au@PtPd enhanced immunoassay with 3D printed smartphone device for quantification of diaminochlorotriazine diaminochlorotrazine(DACT), the major atrazine biomarker

A multimetallic nanozyme enhanced colorimetric biosensor for Salmonella detection on finger-actuated microfluidic chip

Salmonella screening is essential to avoid food poisoning. A simple, fast and sensitive colorimetric biosensor was elaborately developed for Salmonella detection on a microfluidic chip through limiting air chambers for precise air control, switching rotary valves for accurate fluid selection, a convergence-and-divergence passive micromixer and an extrusion-and-suction active micromixer for efficient fluid mixing, and immune gold@platinum palladium nanocatalysts for effective signal amplification. The mixture of bacteria, immune magnetic nanobeads and nanocatalysts was first rapidly mixed to form nanobead-bacteria-nanocatalyst conjugates and magnetically separated for enrichment. After washing with water, the conjugates were used to catalyze colorless substrate and blue product was finally analyzed using ImageJ for quantifying bacterial concentration. The finger-actuated microfluidic chip enabled designated control of designated fluids in designated places towards designated directions by simple press-release operations on designated air chambers without any external power. Under optimal conditions, this sensor could detect Salmonella at 45 CFU/mL in 25 min.

Inclusive and Accurate Clinical Diagnostics Using Intelligent Computation and Smartphone Imaging

Smartphone-based colorimetry has been widely applied in clinical analysis, although significant challenges remain in its practical implementation, including the need to consider biases introduced by the ambient imaging environment, which limit its potential within a clinical decision pathway. In addition, most commercial devices demonstrate variability introduced by manufacturer-to-manufacturer differences. Here, we undertake a systematic characterization of the potential imaging interferences that lead to this limited performance in conventional smartphones and, in doing so, provide a comprehensive new understanding of smartphone color imaging. Through derivation of a strongly correlated parameter for sample quantification, we enable real-time imaging, which for the first time, takes the first steps to turning the mobile phone camera into an analytical instrument - irrespective of model, software, and the operating systems used. We demonstrate clinical applicability through the imaging of patients' skin, enabling rapid and convenient diagnosis of cyanosis and measurement of local oxygen concentration to a level that unlocks clinical decision-making for monitoring cardiovascular disease and anemia. Importantly, we show that our solution also accounts for the differences in individuals' skin tones as measured across the Fitzpatrick scale, overcoming potential clinically significant errors in current optical oximetry.

An all-in-one microfluidic SlipChip for power-free and rapid biosensing of pathogenic bacteria

Point-of-care testing of pathogens is becoming more and more important for the prevention and control of food poisoning. Herein, a power-free colorimetric biosensor was presented for rapid detection of Salmonella using a microfluidic SlipChip for fluidic control and Au@PtPd nanocatalysts for signal amplification. All the procedures, including solution mixing, immune reaction, magnetic separation, residual washing, mimicking catalysis and colorimetric detection, were integrated on this SlipChip. First, the mixture of the bacterial sample, immune magnetic nanobeads (IMBs) and immune Au@PtPd nanocatalysts (INCs), washing buffer and H2O2-TMB chromogenic substrate were preloaded into the sample, washing and catalysis chambers, respectively. After the top layer of this SlipChip was slid to connect the sample chamber with the separation chamber, the mixture was moved back and forth through the asymmetrical split-and-recombine micromixer by using a disposable syringe to form the IMB-Salmonella-INC sandwich conjugates. Then, the conjugates were captured in the separation chamber using a magnetic field, and the top layer was slid to connect the washing chamber with the separation chamber for washing away excessive INCs. Finally, the top layer was slid to connect the catalysis chamber with the separation chamber, and the colorless substrate was catalyzed by the INCs with peroxidase-mimic activity to generate color change, followed by using a smartphone app to collect and analyze the image to determine the bacterial concentration. This all-in-one microfluidic biosensor enabled simple detection of Salmonella as low as 101.2 CFU mL-1 within 30 min and was featured with low cost, straightforward operation, and compact design.

Multiplex nanozymatic biosensing of Salmonella on a finger-actuated microfluidic chip

A colorimetric biosensor was elaboratively designed for fast, sensitive and multiplex bacterial detection on a single microfluidic chip using immune magnetic nanobeads for specific bacterial separation, immune gold@platinum palladium nanoparticles for specific bacterial labeling, a finger-actuated mixer for efficient immunoreaction and two coaxial rotatable magnetic fields for magnetic nanobead capture (outer one) and magnet-actuated valve control (inner one). First, preloaded bacteria, nanobeads and nanozymes were mixed through a finger actuator to form nanobead-bacteria-nanozyme conjugates, which were captured by the outer magnetic field. After the inner magnetic field was rotated to successively wash the conjugates and push the H2O2-TMB substrate for resuspending these conjugates, colorless TMB was catalyzed into blue TMBox products, followed by color analysis using ImageJ software for bacterial determination. This simple biosensor enabled multiplex Salmonella detection as low as 9 CFU per sample in 45 min.

A versatile 3D printed multi-electrode cell for determination of three COVID-19 biomarkers

3D-printing has shown an outstanding performance for the production of versatile electrochemical devices. However, there is a lack of studies in the field of 3D-printed miniaturized settings for multiplex biosensing. In this work, we propose a fully 3D-printed micro-volume cell containing six working electrodes (WEs) that operates with 250 μL of sample. A polylactic acid/carbon black conductive filament (PLA/CB) was used to print the WEs and subsequently modified with graphene oxide (GO), to support protein binding. Cyclic voltammetry was employed to investigate the electrochemical behaviour of the novel multi-electrode cell. In the presence of K₃[Fe(CN)₆], PLA/CB/GO showed adequate peak resolution for subsequent label-free immunosensing. The innovative 3D-printed cell was applied for multiplex voltammetric detection of three COVID-19 biomarkers as a proof-of-concept. The multiple sensors showed a wide linear range with detection limits of 5, 1 and 1 pg mL^-1 for N-protein, S_RBD-protein, and anti-S_RBD, respectively. The sensor performance enabled the selective sequential detection of N protein, S_RBD protein, and anti-S_RBD at biological levels in saliva and serum. In summary, the miniaturized six-electrode cell presents an alternative for the low-cost and fast production of customizable devices for multi-target sensing with promising application in the development of point-of-care sensors.