Ultrasensitive and Rapid Detection of Procalcitonin via Waveguide-Enhanced Nanogold-Linked Immunosorbent Assay for Early Sepsis Diagnosis.

Sepsis, a life-threatening inflammatory response, demands economical, accurate, and rapid detection of biomarkers during the critical "golden hour" to reduce the patient mortality rate. Here, we demonstrate a cost-effective waveguide-enhanced nanogold-linked immunosorbent assay (WENLISA) based on nanoplasmonic waveguide biosensors for the rapid and sensitive detection of procalcitonin (PCT), a sepsis-related inflammatory biomarker. To enhance the limit of detection (LOD), we employed sandwich assays using immobilized capture antibodies and detection antibodies conjugated to gold nanoparticles to bind the target analyte, leading to a significant evanescent wave redistribution and strong nanoplasmonic absorption near the waveguide surface. Experimentally, we detected PCT for a wide linear response range of 0.1 pg/mL to 1 ng/mL with a record-low LOD of 48.7 fg/mL (3.74 fM) in 8 min. Furthermore, WENLISA has successfully identified PCT levels in the blood plasma of patients with sepsis and healthy individuals, offering a promising technology for early sepsis diagnosis.

Slab waveguide-based particle plasmon resonance optofluidic biosensor for rapid and label-free detection.

An effective bio-sensing platform that would meet the criteria of rapid, simple, and sensitive detection is crucial to translate bench research to clinical applications. However, simultaneously rapid and sensitive biosensing remains challenging for practical biomedical applications. In this study, for the first time, we demonstrate a cost-effective, label-free, real-time, and sensitive slab waveguide-based particle plasmon resonance (WGPPR) biosensor for practical clinical applications. A suspended glass slab waveguide structure with excellent optical confinement properties was designed and fabricated as the biosensor. Gold nanoparticles (AuNPs) were deposited on the top surface of the waveguide layer to significantly enhance the optical near field through the localized surface plasmon resonance (LSPR) effect. When light travels through the waveguide, the change in the local refractive index (RI) near the surface of the AuNPs can be transformed into changes in the intensity of transmitted light, thereby enabling sensitive and real-time detection. The RI sensing experiment shows a good sensor resolution of 1.43 × 10-4 RIU, which represents a 395% enhancement compared to that of the sensor without AuNPs. Through biochemical detection experiments, we measured IgG and determined the detection limit (LOD) at 614 ng mL-1 in ∼4 min, thereby proving the feasibility of the bio-detection sensing functionality. This study demonstrates a new type of WGPPR biosensor, which offers several unique advantages such as simple structure, high sensitivity, and rapid bio-sensing for practical bio-medical sensing applications. The new biosensor also fulfils point-of-care (POC) requirements.

Rapid and Highly Sensitive Detection of C-Reaction Protein Using Robust Self-Compensated Guided-Mode Resonance BioSensing System for Point-of-Care Applications.

The rapid and sensitive detection of human C-reactive protein (CRP) in a point-of-care (POC) may be conducive to the early diagnosis of various diseases. Biosensors have emerged as a new technology for rapid and accurate detection of CRP for POC applications. Here, we propose a rapid and highly stable guided-mode resonance (GMR) optofluidic biosensing system based on intensity detection with self-compensation, which substantially reduces the instability caused by environmental factors for a long detection time. In addition, a low-cost LED serving as the light source and a photodetector are used for intensity detection and real-time biosensing, and the system compactness facilitates POC applications. Self-compensation relies on a polarizing beam splitter to separate the transverse-magnetic-polarized light and transverse-electric-polarized light from the light source. The transverse-electric-polarized light is used as a background signal for compensating noise, while the transverse-magnetic-polarized light is used as the light source for the GMR biosensor. After compensation, noise is drastically reduced, and both the stability and performance of the system are enhanced over a long period. Refractive index experiments revealed a resolution improvement by 181% when using the proposed system with compensation. In addition, the system was successfully applied to CRP detection, and an outstanding limit of detection of 1.95 × 10-8 g/mL was achieved, validating the proposed measurement system for biochemical reaction detection. The proposed GMR biosensing sensing system can provide a low-cost, compact, rapid, sensitive, and highly stable solution for a variety of point-of-care applications.

Low-cost planar waveguide-based optofluidic sensor for real-time refractive index sensing.

We report on the design, fabrication, and characterization of mass-producible, sensitive, intensity-detection-based planar waveguide sensors for rapid refractive index (RI) sensing; the sensors comprise suspended glass planar waveguides on glass substrates, and are integrated with microfluidic channels. They are facilely and cost-effectively constructed via vacuum-less processes. They yield a high throughput, enabling mass production. The sensors respond to solutions with different RIs via variations in the transmitted optical power due to coupling loss in the sensing region, facilitating real-time and simple RI detection. Experiments yield a good resolution of 5.65 × 10-4 RIU. This work has major implications for several RI-sensing-based applications.

Silicon-based high-responsivity GeSn short-wave infrared heterojunction phototransistors with a floating base.

We demonstrate silicon-based $p \text{-} n \text{-} p$p-n-p floating-base GeSn heterojunction phototransistors with enhanced optical responsivity for efficient short-wave infrared (SWIR) photodetection. The narrow-bandgap GeSn active layer sandwiched between the $p \text{-} {\rm Ge}$p-Ge collector and $n \text{-} {\rm Ge}$n-Ge base effectively extends the photodetection range in the SWIR range, and the internal gain amplifies the optical response by a factor of more than three at a low driving voltage of 0.4 V compared to that of a reference GeSn $p \text{-} i \text{-} n$p-i-n photodetector (PD). We anticipate that our findings will be leveraged to realize complementary metal-oxide-semiconductor-compatible, sensitive, low driving voltage SWIR PDs in a wide range of applications.