MoS₂ Field-Effect Transistor for Next-Generation Label-Free Biosensors

Biosensors based on field-effect transistors (FETs) have attracted much attention, as they offer rapid, inexpensive, and label-free detection. While the low sensitivity of FET biosensors based on bulk 3D structures has been overcome by using 1D structures (nanotubes/nanowires), the latter face severe fabrication challenges, impairing their practical applications. In this paper, we introduce and demonstrate FET biosensors based on molybdenum disulfide (MoS₂), which provides extremely high sensitivity and at the same time offers easy patternability and device fabrication, due to its 2D atomically layered structure. A MoS₂-based pH sensor achieving sensitivity as high as 713 for a pH change by 1 unit along with efficient operation over a wide pH range (3–9) is demonstrated. Ultrasensitive and specific protein sensing is also achieved with a sensitivity of 196 even at 100 femtomolar concentration. While graphene is also a 2D material, we show here that it cannot compete with a MoS₂-based FET biosensor, which surpasses the sensitivity of that based on graphene by more than 74-fold. Moreover, we establish through theoretical analysis that MoS₂ is greatly advantageous for biosensor device scaling without compromising its sensitivity, which is beneficial for single molecular detection. Furthermore, MoS₂, with its highly flexible and transparent nature, can offer new opportunities in advanced diagnostics and medical prostheses. This unique fusion of desirable properties makes MoS₂ a highly potential candidate for next-generation low-cost biosensors

Controlling the Growth of Staphylococcus epidermidis by Layer-By-Layer Encapsulation

Commensal skin bacteria such as Staphylococcus epidermidis are currently being considered as possible components in skin-care and skin-health products. However, considering the potentially adverse effects of commensal skin bacteria if left free to proliferate, it is crucial to develop methodologies that are capable of maintaining bacteria viability while controlling their proliferation. Here, we encapsulate S. epidermidis in shells of increasing thickness using layer-by-layer assembly, with either a pair of synthetic polyelectrolytes or a pair of oppositely charged polysaccharides. We study the viability of the cells and their delay of growth depending on the composition of the shell, its thickness, the charge of the last deposited layer, and the degree of aggregation of the bacteria which is varied using different coating proceduresamong which is a new scalable process that easily leads to large amounts of nonaggregated bacteria. We demonstrate that the growth of bacteria is not controlled by the mechanical properties of the shell but by the bacteriostatic effect of the polyelectrolyte complex, which depends on the shell thickness and charge of its outmost layer, and involves the diffusion of unpaired amine sites through the shell. The lag times of growth are sufficient to prevent proliferation for daily topical applications

Delivering Nanoparticles to Lungs while Avoiding Liver and Spleen through Adsorption on Red Blood Cells

Nanoparticulate drug delivery systems are one of the most widely investigated approaches for developing novel therapies for a variety of diseases. However, rapid clearance and poor targeting limit their clinical utility. Here, we describe an approach to harness the flexibility, circulation, and vascular mobility of red blood cells (RBCs) to simultaneously overcome these limitations (cellular hitchhiking). A noncovalent attachment of nanoparticles to RBCs simultaneously increases their level in blood over a 24 h period and allows transient accumulation in the lungs, while reducing their uptake by liver and spleen. RBC-adsorbed nanoparticles exhibited ∼3-fold increase in blood persistence and ∼7-fold higher accumulation in lungs. RBC-adsorbed nanoparticles improved lung/liver and lung/spleen nanoparticle accumulation by over 15-fold and 10-fold, respectively. Accumulation in lungs is attributed to mechanical transfer of particles from the RBC surface to lung endothelium. Independent tracing of both nanoparticles and RBCs <i>in vivo</i> confirmed that RBCs themselves do not accumulate in lungs. Attachment of anti-ICAM-1 antibody to the exposed surface of NPs that were attached to RBCs led to further increase in lung targeting and retention over 24 h. Cellular hitchhiking onto RBCs provides a new platform for improving the blood pharmacokinetics and vascular delivery of nanoparticles while simultaneously avoiding uptake by liver and spleen, thus opening the door for new applications

Elasticity of Nanoparticles Influences Their Blood Circulation, Phagocytosis, Endocytosis, and Targeting

The impact of physical and chemical modifications of nanoparticles on their biological function has been systemically investigated and exploited to improve their circulation and targeting. However, the impact of nanoparticles’ flexibility (<i>i.e.</i>, elastic modulus) on their function has been explored to a far lesser extent, and the potential benefits of tuning nanoparticle elasticity are not clear. Here, we describe a method to synthesize polyethylene glycol (PEG)-based hydrogel nanoparticles of uniform size (200 nm) with elastic moduli ranging from 0.255 to 3000 kPa. These particles are used to investigate the role of particle elasticity on key functions including blood circulation time, biodistribution, antibody-mediated targeting, endocytosis, and phagocytosis. Our results demonstrate that softer nanoparticles (10 kPa) offer enhanced circulation and subsequently enhanced targeting compared to harder nanoparticles (3000 kPa) <i>in vivo</i>. Furthermore, <i>in vitro</i> experiments show that softer nanoparticles exhibit significantly reduced cellular uptake in immune cells (J774 macrophages), endothelial cells (bEnd.3), and cancer cells (4T1). Tuning nanoparticle elasticity potentially offers a method to improve the biological fate of nanoparticles by offering enhanced circulation, reduced immune system uptake, and improved targeting

The Effect of Polymeric Nanoparticles on Biocompatibility of Carrier Red Blood Cells

<div><p>Red blood cells (RBCs) can be used for vascular delivery of encapsulated or surface-bound drugs and carriers. Coupling to RBC prolongs circulation of nanoparticles (NP, 200 nm spheres, a conventional model of polymeric drug delivery carrier) enabling their transfer to the pulmonary vasculature without provoking overt RBC elimination. However, little is known about more subtle and potentially harmful effects of drugs and drug carriers on RBCs. Here we devised high-throughput <i>in vitro</i> assays to determine the sensitivity of loaded RBCs to osmotic stress and other damaging insults that they may encounter <i>in vivo</i> (<i>e</i>.<i>g</i>. mechanical, oxidative and complement insults). Sensitivity of these tests is inversely proportional to RBC concentration in suspension and our results suggest that mouse RBCs are more sensitive to damaging factors than human RBCs. Loading RBCs by NP at 1:50 ratio did not affect RBCs, while 10–50 fold higher NP load accentuated RBC damage by mechanical, osmotic and oxidative stress. This extensive loading of RBC by NP also leads to RBCs agglutination in buffer; however, addition of albumin diminished this effect. These results provide a template for analyses of the effects of diverse cargoes loaded on carrier RBCs and indicate that: i) RBCs can tolerate carriage of NP at doses providing loading of millions of nanoparticles per microliter of blood; ii) tests using protein-free buffers and mouse RBCs may overestimate adversity that may be encountered in humans.</p></div

Complement lysis of human RBCs with 200nm nanoparticles adsorbed onto their surface at 1.0% hematocrit.

<p>Hemolytic curves for human RBC/NP:RBCs were obtained after the addition of complement obtain from serum rotating at 37°C for 4h. The addition of streptavidin-biotin (SA-B) was used as a control. Curves were determined for NP:RBC ratio (200:1; 400:1; 2000:1). Values are means (n = 4) ± SD. (**, P<0.01 ***, P<0.001 vs. naïve RBC). Please note that some deviation bars are too small to be evident.</p

Mechanical fragility of red blood cells with 200nm nanoparticles adsorbed onto their surface at 1.0% hematocrit.

<p>Percent hemolysis of mouse NP:RBCs (A) and human NP:RBCs (C) (50:1; 200:1; and 2000:1) were obtained after constant rotation with glass beads at 24 rpm at 37°C for up to 8h and 24h, respectively. Percent hemolysis of different NP:RBC ratios for mouse RBC at 0.5h (B) and human RBC at 2h (D). Values are means (n = 4–5) ± SD. Please note that some deviation bars are too small to be evident.</p

Oxidative fragility of red blood cells with 200nm nanoparticles adsorbed onto their surface at 1.0% hematocrit.

<p>Percent hemolysis of mouse (A,B,C) and human (D,E) RBC/NP:RBCs (50:1; 200:1; and 2000:1) were obtained after rotating at 24 rpm at 37°C for up to 24h and 46h, respectively, after being challenged with 3mM H₂O₂. Percent hemolysis of different NP:RBC ratios for mouse RBC at 4h (B), 24h (C) and human RBC at 32h (E). Values are means (n = 4–5) ± SD. (***,P<0.001 vs naïve RBC). Please note in (D) lysis is caused by adsorption of NPs, not by H₂O₂. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0152074#pone.0152074.g002" target="_blank">Fig 2B</a> for controls without H₂O₂.</p

Osmotic fragility of red blood cells with 200nm nanoparticles adsorbed onto their surface at 1.0% hematocrit.

<p>Hemolytic curves for mouse (A) and human (B) NP:RBCs were obtained after immediate exposure to different [NaCl]. Curves were determined for NP:RBC ratio (50:1, 200:1, and 2000:1). Percent hemolysis of different RBC/NP:RBC ratios at 73mM NaCl (C). Values are means (n = 4–6) ± SD. (***, P<0.001 vs naïve RBC). Please note that some deviation bars are too small to be evident.</p

Effect of low stress over time on red blood cells with 200nm nanoparticles adsorbed onto their surface at 1.0% hematocrit.

<p>Hemolytic curves for mouse (A) and (B) human RBC/NP:RBCs were obtained after constant rotation at 24 rpm at 37°C for up to 46h. Curves were determined for NP:RBC ratio (50:1; 200:1; 2000:1). Percent hemolysis of different NP:RBC ratios at 24h (C). Values are means (n = 5) ± SD. (***, P<0.001 vs naïve mouse RBC) (###,P<0.001 vs naïve human RBC).</p