Effect of a new slow-release zinc fertilizer based on carbon dots on the zinc concentration, growth indices, and yield in wheat (Triticum aestivum).

The present study aimed to introduce a new carbon dots nanocarrier (Zn-NCDs) as a slow-release Zn fertilizer. Zn-NCDs was synthesized using a hydrothermal method and characterized by instrumental methods. A greenhouse experiment was then conducted involving two Zn sources (Zn-NCDs and ZnSO4), three concentrations of Zn-NCDs (2, 4, and 8 mg/L), and under sand culture conditions. This study comprehensively evaluated the effects of Zn-NCDs on the zinc, nitrogen, and phytic acid content, biomass, growth indices, and yield in bread wheat (cv. Sirvan). Also, a fluorescence microscope was used to examine the in vivo transport route of Zn-NCDs in wheat organs. Finally, the availability of Zn in soil samples treated with Zn-NCDs was evaluated over 30 days in an incubation experiment. The findings indicated that Zn-NCDs as a slow-release fertilizer increased root-shoot biomass, fertile spikelet, and grain yield by 20, 44, 16, and 43%, respectively, compared to ZnSO4 treatment. The concentration of zinc and nitrogen in the grain was increased by 19% and 118%, respectively, while phytic acid was decreased by 18% than ZnSO4 treatment. Microscopic observations revealed that wheat plants could absorb and transfer Zn-NCDs from roots to stems and leaves through vascular bundles. This study demonstrated for the first time that Zn-NCDs could be used as a slow-release Zn fertilizer with high efficiency and low cost in wheat enrichment. In addition, Zn-NCDs could be applied as a new nano fertilizer and technology for in vivo plant imaging.

Optofluidic flow meter for sub-nanoliter per minute flow measurements.

SIGNIFICANCE: Performance improvements in microfluidic systems depend on accurate measurement and fluid control on the micro- and nanoscales. New applications are continuously leading to lower volumetric flow rates. AIM: We focus on improving an optofluidic system for measuring and calibrating microflows to the sub-nanoliter per minute range. APPROACH: Measurements rely on an optofluidic system that delivers excitation light and records fluorescence in a precise interrogation region of a microfluidic channel. Exploiting a scaling relationship between the flow rate and fluorescence emission after photobleaching, the system enables real-time determination of flow rates. RESULTS: Here, we demonstrate improved calibration of a flow controller to 1% uncertainty. Further, the resolution of the optofluidic flow meter improved to less than 1 nL / min with 5% uncertainty using a molecule with a 14-fold smaller diffusion coefficient than our previous report. CONCLUSIONS: We demonstrate new capabilities in sub-nanoliter per minute flow control and measurement that are generalizable to cutting-edge light-material interaction and molecular diffusion for chemical and biomedical industries.

Microelectrophoretic single-cell measurements with microfluidic devices.

Here we describe in detail the design, fabrication and operation of our automated high-throughput single cell microchip electrophoresis device with laser induced fluorescence detection. Our device features on-board integrated peristaltic pumps that generate flow directly within the microfluidic channels. Additionally, we have incorporated an optical fiber bridge that enables simultaneous fluorescence detection at two points of interest within the device without the need for additional optical components or detectors. The second detection spot is used to detect the intact cell immediately prior to lysis giving a signal at t=0s for each single-cell electropherogram. We can also use this signal to measure the absolute migration time of the separated analytes to confidently determine the identity of each peak. Finally, we demonstrate the application of our device for the measurement of intracellular nitric oxide (NO) levels in T-lymphocytes. Changes in NO levels within cells is associated with a number of chronic diseases including neurodegenerative, cardiovascular and cancers. We show that our system is capable of measuring NO levels under the following conditions: native, lipopolysaccharide stimulation, and inhibition of inducible nitric oxide synthase. It is our hope that the information and procedures described in this chapter may enable others to use or adapt our system for other analyses at the single cell level.

Out-of-plane integration of a multimode optical fiber for single particle/cell detection at multiple points on a microfluidic device with applications to particle/cell counting, velocimetry, size discrimination and the analysis of single cell lysate injections.

In this paper a single particle/cell-tracking microfluidic device that integrates an out-of-plane multimode optical fiber (OP-MMF) is reported. This OP-MMF is used to generate three excitation light-lines and three detection spots using only one excitation source and one detector. It takes advantage of an optical tunneling mode to create two excitation lines in a microfluidic channel emanating from a single fiber end. This method was used to accurately count particles/cells and perform velocity measurements and size discrimination. The velocity and size distributions of 5, 7, and 10 µm fluorescently labeled polystyrene beads were determined using the OP-MMF. Additionally, this method was used to analyze cell lysates with the third excitation line in the separation channel. The OP-MMF setup accurately detected an intact cell twice ∼2 mm prior to lysis, determined its velocity, and detected the injected cell lysate 3 mm downstream of the injection point in the separation channel. Using this setup, the velocity of cells entering the lysis intersection and the absolute migration times of fluorescently labeled analytes injected into the separation channel were determined in an automated fashion. This method enabled us to determine a lysing/injection efficiency coefficient (K) using signals from the injected lysate signal and from the intact cell before lysing. K provided a reliable measurement of the amount of cell lysate that was injected into the separation channel. The approach reported here could be used in the future to track particles, cells or droplets in a variety of existing microfluidic devices without the need for multiplexed masks, layers, bulky optical elements or complex optical designs.

A label-free infrared opto-fluidic method for real-time determination of flow rate and concentration with temperature cross-sensitivity compensation.

The ability to accurately measure the flow rate, concentration, and temperature in real-time in micro total analysis systems (µTAS) is crucial when improving their practical sensing capabilities within extremely small volumes. Our label-free infrared (1500-1600 nm) opto-fluidic method, presented in this study, utilizes a cantilever-based flow meter integrated with two parallel optical fiber Fabry-Perot interferometers (FPIs). The first FPI serves as an ultra-sensitive flow meter and includes a Fiber Bragg Grating (FBG) tip for localized temperature sensing. The second FPI has a fabricated photopolymer micro-tip for highly sensitive refractive index (RI) determination. In this work, we performed 3-D simulation analysis to characterize cantilever deflection as well as temperature distribution and its effect on the RI. The experimental results from temperature cross-sensitivity analysis lead to real-time measurement resolutions of 5 nL min-1, 1 × 10-6 RIU and 0.05 °C, for the flow rate, refractive index, and temperature, respectively.

Integrating Optical Fiber Bridges in Microfluidic Devices to Create Multiple Excitation/Detection Points for Single Cell Analysis.

A microfluidic device is reported that employs an out-of-plane optical fiber bridge to generate two excitation and two detection spots in a microfluidic channel using only one excitation source and one detector. This fiber optic bridge was integrated into a single cell analysis device to detect an intact cell just prior to lysis and the injected lysate 2, 5, 10, or 15 mm downstream of the injection point. Using this setup the absolute migration times for analytes from cells stochastically entering the lysis intersection could be determined for the first time in an automated fashion. This allowed the evaluation of several separation parameters, including analyte band velocity, migration time drift, diffusion coefficient, injection plug length, separation efficiency (N), and plate height (H), which previously could only be estimated. To demonstrate the utility of this system, a peptide substrate for protein kinase B (PKB) was designed, synthesized, and loaded into T-lymphocytes in order to measure PKB activity in individual cells. The optical fiber bridge is easy to implement, inexpensive, and flexible in terms of changing the distances between the two detection points.

Real-time measurement of flow rate in microfluidic devices using a cantilever-based optofluidic sensor.

Real-time and accurate measurement of flow rate is an important reqirement in lab on a chip (LOC) and micro total analysis system (µTAS) applications. In this paper, we present an experimental and numerical investigation of a cantilever-based optofluidic flow sensor for this purpose. Two sensors with thin and thick cantilevers were fabricated by engraving a 2D pattern of cantilever/base on two polymethylmethacrylate (PMMA) slabs using a CO2 laser system and then casting a 2D pattern with polydimethylsiloxane (PDMS). The basic working principle of the sensor is the fringe shift of the Fabry-Pérot (FP) spectrum due to a changing flow rate. A Finite Element Method (FEM) is used to solve the three dimensional (3D) Navier-Stokes and structural deformation equations to simulate the pressure distribution, velocity and cantilever deflection results of the flow in the channel. The experimental results show that the thin and thick cantilevers have a minimum detectable flow change of 1.3 and 4 (µL min(-1)) respectively. In addition, a comparison of the numerical and experimental deflection of the cantilever has been done to obtain the effective Young's modulus of the thin and thick PDMS cantilevers.

Measurement and control of pressure driven flows in microfluidic devices using an optofluidic flow sensor.

Measurement and control of pressure-driven flow (PDF) has a great potential to enhance the performance of chemical and biological experiments in Lab on a Chip technology. In this paper, we present an optofluidic flow sensor for real-time measurement and control of PDF. The optofluidic flow sensor consists of an on-chip micro Venturi and two optical Fabry-Pérot (FP) interferometers. Flow rate was measured from the fringe shift of FP interferometers resulted from movement fluid in the on-chip micro Venturi. The experimental results show that the optofluidic flow sensor has a minimum detectable flow change of 5 nl/min that is suitable for real time monitoring and control of fluids in many chemical and biological experiments. A Finite Element Method is used to solve the three dimensional (3D) Navier-Stokes and continuity equations to validate the experimental results.