Salicylate Urinalysis Chip

Geometry

Top view of the Salicylate Urinalysis Chip, generated from OpenSCAD source

Isometric view of the Salicylate Urinalysis Chip, generated from OpenSCAD source

Top view (left) and isometric view (right) of the placed-and-routed chip. Rendered with OpenSCAD from the chip’s SCAD source, salicylic_acid_reroute.scad. Click for high-resolution.

Download: PNG (top) · PNG (iso) · SCAD source ↓

Specifications

Inputs: 4 (soln1, soln2, soln3, soln4)
Outputs: 1 (out)
Mixers: 3 × diffmix_25px_0
Serpentine channels: 4 (parametric p_serpentine variants — see pcell manifest)
Substrate: 2550 × 1600 × 230 (h.r.3.3 PDK)
Standard cells: diffmix_25px_0, p_serpentine
Status: H.R.3.3 design, made by the design software

Assay

This chip is designed to measure urinary salicylate concentration via the Trinder colorimetric reaction. Acidic ferric nitrate reacts with salicylate to form a violet ferric salicylate complex whose absorbance is measured spectrophotometrically; the absorbance is proportional to the salicylate concentration in the original sample.

Clinically, urinary salicylate quantification supports NSAID monitoring, aspirin overdose detection, and routine follow-up of chronic salicylate users (e.g. patients on long-term low-dose aspirin or arthritis regimens).

The chemistry is adapted from the Beckman Coulter AU480 reagent kit BASOSR7S229 (Salicylic Acid). The chip implements passive resistance-metering to combine the urine sample with three reagent streams at the volumetric ratios required by the Trinder protocol; the output channel collects the mixed product for off-chip spectrophotometric readout.

Simulated outlet concentrations

From the pipeline’s circuit simulation. Nothing here was measured.

This table is output of the pipeline’s circuit simulation (Xyce), written by its evaluation step. For each input it gives the concentration the simulation reaches at the chip’s outlet, out, at time 0.0 in the file, against the concentration the design targets there. No analyzer and no urine sample are involved.

Input	Node	Error	Target conc.	Simulated conc.
`sample`	`out`	2.90 %	0.012605	0.012239
`H2O`	`out`	0.37 %	0.042017	0.042171
`R2`	`out`	2.94 %	0.315126	0.324403
`R1`	`out`	1.44 %	0.630252	0.621187

Source: Chem_Eval.csv. Concentrations are fractions of the mixed stream at the outlet (sample + H2O + R1 + R2 sum to 1.0); Error is the simulated concentration’s relative deviation from the design’s target.

Files

SCADsalicylic_acid_reroute.scad1.8 MBDownload
LEFh.r.3.3_salicylic_acid_pcells.lef2.4 KBDownload
CSVpcell_out_scad266 BDownload
CSVChem_Eval.csv309 BDownload
GUIDEroute.guide2.7 KBDownload
PNGsalicylic_acid_iso_large.png123.9 KBDownload
PNGsalicylic_acid_top_large.png19.3 KBDownload

salicylic_acid_reroute.scad is the placed-and-routed 3D geometry — the main OpenSCAD source for this chip. h.r.3.3_salicylic_acid_pcells.lef contains chip-specific cell abstracts. pcell_out_scad lists the parametric serpentine-channel variants this chip required (with L1 / L2 / turn count). Chem_Eval.csv is the pipeline’s simulation of the outlet concentrations, shown above. route.guide is the OpenROAD routing guide produced during PNR. The PNG renders are high-resolution versions of the views shown in the Geometry section above.

Papers

Related methodology archetype

Goenner, B., Temple, S., Zapata, S., Wakeham, D., Snelgrove, A., Gaillardon, P.-E., Nordin, G. P., & Gale, B. K. (2025). An open source platform to automate the design, verification, and manufacture of 3D printed microfluidic devices. Scientific Reports, 15, 33077. DOI: 10.1038/s41598-025-15976-9

Applications

For research use only. Not for use in diagnostic procedures.

A design for urinary salicylate quantification by the Trinder method, the kind of assay used for NSAID monitoring and aspirin-overdose detection. The table above is a simulation. One of the urinalysis chip designs in the Gale Lab urinalysis chip family (Erica Francis).