Persistent drought monitoring using a microfluidic-printed electro-mechanical sensor of stomata

Stomatal function can be used effectively to monitor plant hydraulics, photosensitivity, and gas exchange. Current approaches to measure single stomatal aperture, such as mold casting or fluorometric techniques, do not allow real time or persistent monitoring of the stomatal function over timescales relevant for long term plant physiological processes, including vegetative growth and abiotic stress. Herein, we utilize a nanoparticle-based conducting ink that preserves stomatal function to print a highly stable, electrical conductometric sensor actuated by the stomata pore itself, repeatedly and reversibly for over 1 week. This stomatal electro-mechanical pore size sensor (SEMPSS) allows for real-time tracking of the latency of single stomatal opening and closing times in planta, which we show vary from 7.0 ± 0.5 to 25.0 ± 0.5 min for the former and from 53.0 ± 0.5 to 45.0 ± 0.5 min for the latter in Spathiphyllum wallisii. These values are shown to correlate with the soil water potential and the onset of the wilting response, in quantitative agreement with a dynamic mathematical model of stomatal function. A single stoma of Spathiphyllum wallisii is shown to distinguish between incident light intensities (up to 12 mW cm−2) with temporal latency slow as 7.0 ± 0.5 min. Over a seven day period, the latency in opening and closing times are stable throughout the plant diurnal cycle and increase gradually with the onset of drought. The monitoring of stomatal function over long term timescales at single stoma level will improve our understanding of plant physiological responses to environmental factors

Surface functionalization-specific binding of coagulation factors by zinc oxide nanoparticles delays coagulation time and reduces thrombin generation potential <i>in vitro</i>

<div><p>Zinc oxide nanoparticles (ZnO NPs) have many biomedical applications such as chemotherapy agents, vaccine adjuvants, and biosensors but its hemocompatibility is still poorly understood, especially in the event of direct contact of NPs with blood components. Here, we investigated the impact of size and surface functional groups on the platelet homeostasis. ZnO NPs were synthesized in two different sizes (20 and 100 nm) and with three different functional surface groups (pristine, citrate, and L-serine). ZnO NPs were incubated with plasma collected from healthy rats to evaluate the coagulation time, kinetics of thrombin generation, and profile of levels of coagulation factors in the supernatant and coronated onto the ZnO NPs. Measurements of plasma coagulation time showed that all types of ZnO NPs prolonged both active partial thromboplastin time and prothrombin time in a dose-dependent manner but there was no size- or surface functionalization-specific pattern. The kinetics data of thrombin generation showed that ZnO NPs reduced the thrombin generation potential with functionalization-specificity in the order of pristine > citrate > L-serine but there was no size-specificity. The profile of levels of coagulation factors in the supernatant and coronated onto the ZnO NPs after incubation of platelet-poor plasma with ZnO NPs showed that ZnO NPs reduced the levels of coagulation factors in the supernatant with functionalization-specificity. Interestingly, the pattern of coagulation factors in the supernatant was consistent with the levels of coagulation factors adsorbed onto the NPs, which might imply that ZnO NPs simply adsorb coagulation factors rather than stimulating these factors. The reduced levels of coagulation factors in the supernatant were consistent with the delayed coagulation time and reduced potential for thrombin generation, which imply that the adsorbed coagulation factors are not functional.</p></div

Western blot analysis of ZnO NP-bound coagulation factors on the surface of NPs.

<p>ZnO NPs were incubated with PPP and NP pellets were collected and dissolved in loading buffer, then analyzed for coagulation factors using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting. Each factor was separately subjected to densitometric analysis.</p

Physicochemical properties of ZnO NP.

<p>Physicochemical properties of ZnO NP.</p

The levels of coagulation factors in the supernatant of platelet poor plasma after incubation with ZnO NPs.

<p><b>ZnO NPs at 0.5 mg/mL were incubated with PPP and the levels of coagulation factors were measured using ELISA kits in the NP-free supernatant.</b> (A), factor II; (B), factor III; (C), factor V; (D), factor VII; (E), factor VIII; (F), factor IX; (G), factor X; (H), factor XI; (I), factor XII. *<i>p</i> < 0.05 and <i>n</i> = 4.</p

Measurement of active partial thromboplastin time and prothrombin time after incubation of platelet-poor plasma and ZnO NPs.

<p>aPTT was measured for (A) 20 nm- and (B) 100 nm-sized ZnO NPs. PT was measured for (C) 20 nm- and (D) 100 nm-sized ZnO NPs. ZnO NPs were conjugated with none (pristine), citrate, and L-serine to provide three distinctive charged surfaces. Each sample was analyzed in duplicate and repeated three times, by using three separate plasma sets. Results are means ± SEM, *<i>p</i> < 0.05 versus control.</p

Summary of expression profile of coagulation factors observed by ELISA and western blot analysis.

<p>Summary of expression profile of coagulation factors observed by ELISA and western blot analysis.</p

Thrombin generation assay of ZnO NPs in platelet poor plasma.

<p>Thrombin generation assay was performed with 20 nm-sized ZnO NPs at (A) 0.1, (B) 0.25, and (C) 0.5 mg/mL. Thrombin generation assay was also performed with 100 nm-sized ZnO NPs at (C) 0.1, (D) 0.25, and (E) 0.5 mg/mL. <i>n</i> = 3.</p

Scanning electron microscopy (SEM) images of ZnO NPs.

<p>(A) Pristine 20 nm, (B) Citrate 20 nm, (C) L-serine 20 nm, (D) Pristine 100 nm, (E) Citrate 100 nm, and (F) L-serine 100 nm.</p