A reminder of picturesque Mississippi

Photograph: Emmett Till Interpretive Center

A sign riddled with bullet holes marks the spot where, in 1955, 14-year-old Emmett Till’s mutilated body was pulled from Mississippi’s Tallahatchie River. Two white men lynched Till for allegedly flirting with a white woman. Site markers such as this one were defaced and replaced repeatedly until 2019, when a 500-pound steel sign—bulletproof and indestructible— was installed.

Emmett Till was lynched a few months after I graduated from high school. I remember the news stories – in most of the North – as clearly as anything else about that summer. The so-called trial of the men who murdered that 14-year-old Black youth found them Not Guilty.

Bacteria-sized robots crush microplastic particles

Metallic microrobots (dark blue dots) colonize a jagged piece of microplastic under visible light, breaking down the plastic

Small pieces of plastic are everywhere, stretching from urban environments to pristine wilderness. Left to their own devices, it can take hundreds of years for them to degrade completely…In a proof-of-concept study, researchers reporting in ACS Applied Materials & Interfaces developed self-propelled microrobots that can swim, attach to plastics and break them down.

…Previous researchers proposed a low-energy way to get rid of plastics in the environment by using catalysts that use sunlight to produce highly reactive compounds that break down these types of polymers. However, getting the catalysts and tiny plastic pieces in contact with each other is challenging and usually requires pretreatments or bulky mechanical stirrers, which aren’t easily scaled-up. Martin Pumera and colleagues wanted to create a sunlight-propelled catalyst that moves toward and latches onto microparticles and dismantles them.

To transform a catalytic material into light-driven microrobots, the researchers made star-shaped particles of bismuth vanadate and then evenly coated the 4-8 μm-wide structures with magnetic iron oxide. The microrobots could swim down a maze of channels and interact with microplastic pieces along their entire lengths. The researchers found that under visible light, microrobots strongly glommed on to four common types of plastics. The team then illuminated pieces of the four plastics covered with the microrobot catalyst for seven days in a dilute hydrogen peroxide solution. They observed that the plastic lost 3% of its weight and that the surface texture for all types changed from smooth to pitted, and small molecules and components of the plastics were found in the left-over solution. The researchers say the self-propelled microrobot catalysts pave the way toward systems that can capture and degrade microplastics in hard-to-reach-locations.

And in a parallel development, Columbia University scientists have built prototype microrobots – called “motes” – that are only 1 cubic millimeter in size. Who knows? Maybe we can yet succeed in magnetizing conspiracy theory antivax nutballs?