The unique properties of NV centers in diamond nanoparticles enable selective identification within organisms and other complex environmental matrices.

While there is great interest in understanding the fate and transport of nanomaterials in the environment and in biological systems, the detection of nanomaterials in complex matrices by fluorescence methods is complicated by photodegradation, blinking, and the presence of natural organic material and other fluorescent background signals that hamper detection of fluorescent nanomaterials of interest. Optically detected magnetic resonance (ODMR) of nitrogen-vacancy (N) centers in diamond nanoparticles provides a pathway toward background-free fluorescence measurements, as the application of a resonant microwave field can selectively modulate the intensity from N centers in nanodiamonds of various diameters in complex materials systems using on-resonance and off-resonance microwave fields. This work represents the first investigation showing how nanoparticle diameter impacts the N center lifetime and thereby directly impacts the accessible contrast and signal-to-noise ratio when using ODMR to achieve background-free imaging of Nnanodiamonds in the presence of interfering fluorophores. These results provide new insights that will guide the choice of optimum nanoparticle size and methodology for background-free imaging and sensing applications, while also providing a model system to explore the fate and transport of nanomaterials in the environment.

Hydrothermal reaction of metal oxalate (ox) salts and bis­(4-pyridylmethyl)­piperazine (bpmp) afforded a series of coordination polymers that were structurally characterized by single-crystal X-ray diffraction. {[Cd­(H2O)4(bpmp)]­(ox)} n (1) and {[Co­(H2O)4(bpmp)]­(ox)} n (2) show isostructural cationic one-dimensional (1D) coordination polymer chain motifs with unligated ox anions. A higher temperature polymorph of 2, {[Co­(ox)­(bpmp)]·3H2O} n (3), possesses a system of threefold interpenetrated three-dimensional (3D) diamondoid nets. {[Mn­(H2O)4(bpmp)] [Mn2(ox)3]·5H2O} n (4) manifests a unique 1D + 2D → 3D polyrotaxane coordination polymer structure with 1D cationic [Mn­(H2O)4(bpmp)] n chains threaded through apertures coursing through parallel stacks of anionic [Mn2(ox)3] n two-dimensional (2D) hexagonal layers. {[Cu2(ox)2(bpmp)]·6H2O} n (5) possesses 2D [Cu2(ox)2] n layers pillared by bpmp ligands into a 3D [Cu2(ox)2(bpmp)] n coordination polymer network with an unprecedented 4,4-connected self-penetrated (5383)2(5482) topology. Variable temperature magnetic susceptibility studies showed weak antiferromagnetic coupling along [Co­(ox)] n chain submotifs in 3 with concomitant zero-field splitting (J = −4.1(7) cm–1, D = 34.5(6) cm–1), weak antiferromagnetic coupling within the [Mn2(ox)3] n hexagonal layers in 4 (J ∼ −0.5 cm–1), and strong antiferromagnetic coupling within the 2D [Cu2(ox)2] n layers in 5 (J = −220(6) cm–1).