Since the 2013 Nobel Prize was awarded for the discovery of vesicle trafficking, a subgroup of nanovesicles called exosomes has been driving the research field to a new regime for understanding cellular communication. This exosome-dominated traffic control system has increased understanding of many diseases, including cancer metastasis, diabetes, and HIV. In addition to the important diagnostic role, exosomes are particularly attractive for drug delivery, due to their distinctive properties in cellular information transfer and uptake. Compared to viral and non-viral synthetic systems, the natural, cell-derived exosomes exhibit intrinsic payload and bioavailability. Most importantly, exosomes easily cross biological barriers, obstacles that continue to challenge other drug delivery nanoparticle systems. Recent emerging studies have shown numerous critical roles of exosomes in many biological barriers, including the blood–brain barrier (BBB), blood–cerebrospinal fluid barrier (BCSFB), blood–lymph barrier (BlyB), blood–air barrier (BAB), stromal barrier (SB), blood–labyrinth barrier (BLaB), blood–retinal barrier (BRB), and placental barrier (PB), which opens exciting new possibilities for using exosomes as the delivery platform. However, the systematic reviews summarizing such discoveries are still limited. This review covers state-of-the-art exosome research on crossing several important biological barriers with a focus on the current, accepted models used to explain the mechanisms of barrier crossing, including tight junctions. The potential to design and engineer exosomes to enhance delivery efficacy, leading to future applications in precision medicine and immunotherapy, is discussed.

Frequent outbreaks of food-borne pathogens, particularly E. coli O157:H7, continue to impact human health and the agricultural economy tremendously. The required cell count for this pathogenic strain of E. coli O157:H7 is relatively low and hence it is vital to detect at low colony forming unit (CFU) counts. Available detection methods, though sensitive, fall short in terms of timeliness and often require extensive sample processing. To overcome these limitations, we propose a novel magneto-plasmonic nanosensor (MPnS) by integrating surface plasmon resonance (SPR) properties with spin–spin magnetic relaxation (T2 MR) technology. We engineered MPnS by encapsulating several gold nanoparticles (GNPs) within the polymer-coating of iron oxide nanoparticles (IONPs). First, the polyacrylic acid (PAA)-coated IONPs were synthesized using a solvent precipitation method, then gold chloride solution was used to synthesize GNPs and encapsulate them within the PAA-coatings of IONPs in one step. A magnetic separation technique was used to purify the MPnS and the presence of GNPs within IONPs was characterized using transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and other spectroscopic methods. The synthesized MPnS exhibits MR relaxation properties while possessing amplified optical properties than conventional GNPs. This allows for rapid and ultrasensitive detection of E. coli O157:H7 by SPR, T2 MR, and colorimetric readout. Experiments conducted in simple buffer and in milk as a complex media demonstrated that our MPnS-based assay could detect as low as 10 CFUs of this pathogenic strain of E. coli O157:H7 in minutes with no cross-reactivity. Overall, the formulated MPnS is robust and holds great potential for the ultrasensitive detection of E. coli O157:H7 in a simple and timely fashion. Moreover, this platform is highly customizable and can be used for the detection of other foodborne pathogens.

Global emergence of the Zika virus and efforts to contain the geographic expansion The Zika virus (ZIKV) was overlooked as a potential threat for more than half a century. It was discovered first in a Rhesus monkey in 1947 in the Zika Forest of Uganda, hence its name, but not until its emergence in 2007 did the flavivirus grab the attention of researchers [1]. Originally, it was thought that the infection was isolated to only sporadic appearances in Asia and Africa, but this idea quickly changed with the first infections documented outside of its regional endemicity [1]. With an estimated three-fourths of the residents of the Confederated States of Micronesia in Yap Island affected [2], ZIKV went from a tropical infection to a potential health risk. The virus, however, classified with other flaviviruses, such as dengue (DENV), yellow fever (YFV), and chikungunya (CHIKV), seemed to be relatively harmless, being selflimiting and presenting with only mild symptoms similar to influenza [2]. Studies documented that around 80% of those infected were asymptomatic, and in fact, most infected today may not even know they have it [3]. However, since then, ZIKV has transitioned from a minor concern to a global health emergency [4]. Not only has it spread rapidly to other countries, but there are more data evidencing causal relationships to neurological disorders in unborn children with infected mothers, as well as more recent evidence supporting a link between ZIKV and neurological disorders in adults [5]. Because it is mainly asymptomatic and because of the grave consequences this can have on developing fetuses, the virus has come under global investigation, with the World Health Organization (WHO) officially declaring ZIKV a Public Health Emergency of International Concern (PHEIC) in 2016 [6]. Prior to 2014, there were no documented ZIKV infections in the Americas, but by 2016, there were 170,000 confirmed cases and 515,000 suspected ones, although numbers as high as 1.9 million suspected cases have been estimated for the same time period [7, 8]. Pathogenicity on the population level is being analyzed to understand, prevent, and treat this emerging disease. By October 2016, ZIKV outbreaks were being reported in more than 60 countries, with 1 million cases alone in Brazil [4]. These figures continued to increase at an alarming rate, with estimates ranging from 35 countries [3] to as many as 84 countries from the beginning of 2016 to 2017 [9]. Of great concern is the evidence accruing validating the hypothesis that ZIKV is causally linked to microcephaly and other neurological disorders in newborns, fetal malformation [4], and now Guillain-Barre ´syndrome (GBS) in adults [5]. According to WHO, by March 2017, 23 countries or territories had reported an increase in GBS cases, suggesting a causal link to ZIKV, and 31 had reported increases in central nervous system malformations, with preliminary evidence associating this with ZIKV infection [9]. The virus, spread commonly through the mosquito vector Aedes aegypti, also can be transmitted through sexual contact as well as through blood transfusions [3, 4]. The arbovirus is also