The Invisibles

Trained dogs have demonstrated:

Your entire blood volume passes through the lungs every 60 seconds. Click a biomarker to isolate; click “All VOCs” for full breath:

Emotional tears contain leucine-enkephalin—a natural opioid painkiller—plus prolactin and adrenocorticotropic hormone. Reflex tears (from onions, wind) lack these entirely. Crying is biochemical self-medication, and a chemical signal to those around you.

385 compounds from skin—more than any other source. Androstadienone in male sweat alters hypothalamic activity below conscious smell.

Over 1,000 proteins identified. Your mouth is one of the richest diagnostic sites—no needle required.

But saliva is not just your chemistry. It is the chemistry of a civilisation. Over 700 species of bacteria, fungi, archaea, and viruses inhabit the oral cavity—a microbiome second only to the gut in diversity. Walt Whitman wrote, “I am large, I contain multitudes.” He was more literally correct than he knew. We are not singular organisms. We are ecosystems—bodies singing the social electric, larger inside than we imagine ourselves to be outside.

This interior ecology is fragile. A recent study found that vaping reshapes the subgingival microbiome in ways eerily parallel to smoking: beneficial taxa decline, inflammatory species proliferate, lipid metabolism and xenobiotic degradation pathways activate—and the disruption scales with puff volume. What you inhale, the multitude inside you reads.

Which raises a tantalising question: if we could see what was happening in this ecosystem in real time, could we also learn to tend it? Companies like Nihl are beginning to explore exactly this—evolving the oral microbiome not by killing bacteria with antiseptic rinses, but by introducing engineered strains that shift the community toward health. The mouth as a garden, not a battlefield.

Blood is central dispatch—65 VOCs identified, plus cell-free DNA that escapes from tumours and circulates months before any scan can find the source. But blood keeps its secrets behind a needle.

What makes blood remarkable is the timeline. Liquid biopsy can detect cancer signals long before symptoms appear:

Then there is troponin—perhaps the single most dramatic molecule in emergency medicine. Normally locked inside heart muscle cells, cardiac troponin I and T escape into the bloodstream only when those cells are damaged. In the ER, when someone arrives with chest pain, the troponin test is what settles the question: heart attack or not.

Levels rise within 2–3 hours of cardiac injury, peak at 18–24 hours, and remain elevated for up to 14 days—a molecular record of damage that persists long after the pain subsides. High-sensitivity assays, now 1,000x more sensitive than the originals introduced in 1995, can detect single-digit nanograms per litre, ruling out heart attacks in under three hours. Roughly 20% of all ER patients receive a troponin test; only 5–10% of those tested are ultimately diagnosed with myocardial infarction. Troponin is used overwhelmingly as a rule-out test—a molecular reassurance.

Breath, skin, tears, saliva broadcast publicly. Blood keeps the private record—and troponin is the alarm that sounds when the record is being written in real time.

A team in flow shares androstadienone, metabolites, oxytocin—chemically, a single organism.

NK cells are our frontline against viruses and cancer. In Li’s controlled studies, participants who walked in forests showed a 50% increase in NK cell activity lasting up to 30 days—while controlling for exercise, diet, and alcohol. The difference was the air itself: α-pinene and 1,8-cineole increase perforin, granzyme A, and granulysin, the cytolytic proteins NK cells use to destroy compromised cells. The forest is not merely calming. It reprograms the body’s stress architecture.

Dr. Ming Kuo’s research at the University of Illinois has demonstrated these effects extend to built environments: green schoolyards measurably improve children’s concentration, reduce ADHD symptoms, and boost classroom engagement. Her work helped catalyse a $10 million tree-planting initiative in Chicago and shaped federal landscaping guidelines. The biological pathways the forest uses—phytoncides, visual fractals, acoustic shelter—are available even in modest urban greenery.

For a beautiful meditation on how we co-evolved with forests: Richard Powers, The Overstory (Pulitzer Prize, 2019).

David Baker’s lab used AI to design de novo protein sensors—molecular velcro for specific biomarkers like lactate (which signals you’re in an anaerobic state). The Silklab stabilised them in silk on a paper patch, they added a chromogenic element. Now you get a paper patch that changes colour when it detects the marker that signals you’re burning muscle without enough oxygen, just by glancing at your arm.

Now to the speculative future: What if you replace the silicon dioxide insulating layer of a transistor with silk embedded with biological sensors? Ions meet electrons. Might we have a Bio-to-Digital transducer—at the scale and cost of microchips?

Your phone, clothes, a sticker on your garden plants—all could sense the hidden biology we are awash within.

A dog detects cancer on a leg. A team locks into chemical synchrony. A forest reprograms immunity for a month. And now, silk-stabilised protein sensors on silicon open a doorway to seeing all of it.

Marcel Proust sensed it in a madeleine soaked in tea—that taste, our oldest sense, connects us to something vast and hidden. We are building the instruments to see the rest:

“What happens when ions meet electrons meet minds?”