Highly Accurate Pneumatically Tunable Optofluidic Distributed Feedback Dye Lasers

Optofluidic dye lasers integrated into microfluidic chips are promising miniature coherent light sources for biosensing. However, achieving the accurate and efficient tuning of lasers remains challenging. This study introduces a novel pneumatically tunable optofluidic distributed feedback (DFB) dye laser in a multilayer microfluidic chip. The dye laser device integrates microfluidic channels, grating structures, and vacuum chambers. A second-order DFB grating configuration is utilized to ensure single-mode lasing. The application of vacuum pressure to the chambers stretches the soft grating layer, enabling the sensitive tuning of the lasing wavelength at a high resolution of 0.25 nm within a 7.84 nm range. The precise control of pressure and laser tuning is achieved through an electronic regulator. Additionally, the integrated microfluidic channels and optimized waveguide structure facilitate efficient dye excitation, resulting in a low pump threshold of 164 nJ/pulse. This pneumatically tunable optofluidic DFB laser, with its high-resolution wavelength tuning range, offers new possibilities for the development of integrated portable devices for biosensing and spectroscopy.

Highly Efficient On-Chip Photothermal Cell Lysis for Nucleic Acid Extraction Using Localized Plasmonic Heating of Strongly Absorbing Au Nanoislands

Cell lysis serves as an essential role in the sample preparation for intracellular material extraction in lab-on-a-chip applications. However, recent microfluidic-based cell lysis chips still face several technical challenges such as reagent removal, complex design, and high fabrication cost. Here, we report highly efficient on-chip photothermal cell lysis for nucleic acid extraction using strongly absorbed plasmonic Au nanoislands (SAP-AuNIs). The highly efficient photothermal cell lysis chip (HEPCL chip) consists of a PDMS microfluidic chamber and densely distributed SAP-AuNIs with large diameters and small nanogaps, allowing for broad-spectrum light absorption. The SAP-AuNIs induce photothermal heat, resulting in a uniform temperature distribution within the chamber and rapidly reaching the target temperature for cell lysis within 30 s. Furthermore, the localized plasmonic heating of SAP-AuNIs expeditiously triggers phase transition and photoporation in the directly contacted lipid bilayer of the cell membrane, resulting in rapid and highly efficient cell lysis. The HEPCL chip successfully lysed 93% of PC9 cells at 90 °C for 90 s without nucleic acid degradation. This on-chip cell lysis offers a new sample preparation platform for integrated point-of-care molecular diagnostics.

Noninvasive Optical Isolation and Identification of Circulating Tumor Cells Engineered by Fluorescent Microspheres

Circulating tumor cells (CTCs) are rare, meaning that current isolation strategies can hardly satisfy efficiency and cell biocompatibility requirements, which hinders clinical applications. In addition, the selected cells require immunofluorescence identification, which is a time-consuming and expensive process. Here, we developed a method to simultaneously separate and identify CTCs by the integration of optical force and fluorescent microspheres. Our method achieved high-purity separation of CTCs without damage through light manipulation and avoided additional immunofluorescence staining procedures, thus achieving rapid identification of sorted cells. White blood cells (WBCs) and CTCs are similar in size and density, which creates difficulties in distinguishing them optically. Therefore, fluorescent PS microspheres with high refractive index (RI) are designed here to capture the CTCs (PS-CTCs) and increase the average index of refraction of PS-CTCs. In optofluidic chips, PS-CTCs were propelled to the collection channel from the sample mixture, under the radiation of light force. Cells from the collection outlet were easily identified under a fluorescence microscope due to the fluorescence signals of PS microspheres. This method provides an approach for the sorting and identification of CTCs, which holds great potential for clinical applications in early diagnosis of disease.

Highly Sensitive, Label-Free Detection of 2,4-Dichlorophenoxyacetic Acid Using an Optofluidic Chip

A highly sensitive approach for rapid and label-free detection of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) using an optofluidic chip is demonstrated. The optofluidic chip is prepared by covalent immobilization of 2,4-D-bovine serum albumin (2,4-D-BSA) conjugate to an integrated microring resonator. Subsequent detection of 2,4-D carried out in a competitive immunoreaction format enables selective detection of 2,4-D in different types of water samples, including bottled, tap, and lake water, at a limit of detection (LOD) of 4.5 pg/mL and in a quantitative range of 15-10⁵ pg/mL. The microring resonator-based optofluidic chip is reusable with ultrahigh sensitivity that offers real-time and on-site detection of low-molecular-weight targets for potential applications in food safety and environmental monitoring.