3D-Printed Biosensor Utilizing a Self-Assembled Near-IR Cyanine Dye for Chromium Detection in Absolute Aqueous Media: Integrated Experimental, Theoretical, and Biological Studies

A near-infrared (NIR) sulfo-cyanine-based dye, 1,1′-bis(3-sulfopropyl)-3,3,3′,3′-tetramethyl-4,5-(1,3-propanediyl)dibenzo[e]indolocarbocyanine (BDC), was developed as a multifunctional fluorescent chemosensor for the selective detection of Cr3+ and biomacromolecules in pure aqueous media. Coordination with Cr3+ induced a decrease in fluorescence at 764 nm and absorbance at 630 nm, with an association constant of 2 × 105 M–1 and a detection limit of 5.11 μM. DFT, Job’s plot, mass spectrometry, and spectroscopic analyses confirmed the binding mechanism. Real-sample tests in tap, river, and lake water showed detection limits of 2–4.4 ppb, demonstrating a high environmental applicability. BDC also exhibited strong binding toward ovalbumin, ct-DNA, and BSA with detection limits of 5 × 10–3, 1.46, and 4 × 10–3 μM, respectively. Owing to its NIR emission, BDC showed efficient cellular penetration and notable anticancer activity against MCF-7 cells. A 3D-printed thermoplastic polyurethane (TPU) biosensor incorporating BDC enabled portable, reversible, and smartphone-assisted colorimetric sensing of Cr3+, consistent with solution-phase results. These results highlight the multifunctional capability and superior practical utility of BDC in environmental and biological applications.